HOW LONG CAN A SOLAR BATTERY LAST DURING A POWER OUTAGE?

One of the most important questions when installing a solar power system is how long the battery will keep your home or business running when electricity from the grid goes off.

The answer depends on several factors.

A solar battery does not have one fixed backup duration simply because it is labelled 5kWh, 10kWh, 15kWh or 20kWh. The actual backup time depends on the battery's usable capacity, the amount of power being consumed, inverter efficiency, battery chemistry, allowable depth of discharge, temperature, battery age, and whether solar panels continue producing energy during the outage.

For example, a 10kWh battery could last many hours when supplying only essential loads such as lights, Wi-Fi, CCTV, television and refrigeration. The same battery could be depleted much faster if it is supplying an electric cooker, kettle, iron, water heater, air conditioner or other high-power appliances.

For professional solar battery sizing, hybrid solar installation, battery replacement, inverter installation and backup-power assessment in Kenya, contact 0723763173.

WHAT DETERMINES BATTERY BACKUP TIME?

The basic relationship is:

Backup time = Usable battery energy ÷ Load power

For example, if a battery provides 10kWh of usable energy and the connected load averages 1kW:

10kWh ÷ 1kW = approximately 10 hours.

If the average load is 2kW:

10kWh ÷ 2kW = approximately 5 hours.

If the average load is 5kW:

10kWh ÷ 5kW = approximately 2 hours.

These are simplified calculations.

Real-world backup time is affected by inverter losses, battery limits, operating conditions and the actual variation in household consumption.

BATTERY KWH IS NOT THE SAME AS KW

This distinction is extremely important.

kWh measures energy storage.

kW measures power.

A 10kWh battery describes approximately how much energy the battery can store.

A 5kW inverter describes approximately how much AC power the inverter can deliver under its operating conditions.

A 10kWh battery does not automatically mean it can run a 10kW appliance.

Likewise, a 5kW inverter does not mean the battery stores 5kWh.

They perform different functions.

A SIMPLE EXAMPLE

Suppose a home has:

10kWh battery

and its essential loads consume an average of:

1kW

A simplified calculation gives:

10 ÷ 1 = 10 hours.

But if inverter and battery losses reduce the usable energy, actual backup could be shorter.

If the household increases the average load to 2kW:

10 ÷ 2 = 5 hours.

At 3kW:

10 ÷ 3 = approximately 3.3 hours.

At 4kW:

10 ÷ 4 = approximately 2.5 hours.

This demonstrates why reducing unnecessary loads can dramatically increase backup duration.

USABLE BATTERY CAPACITY

The number printed on a battery is not necessarily the amount of energy you should expect to use continuously.

For example, a battery may be rated at 10kWh.

Depending on the battery technology and manufacturer's recommended operating limits, the system may use only a portion of that capacity under normal operation.

The usable energy depends on:

Depth of discharge
Battery-management settings
Manufacturer recommendations
Temperature
Battery age
Discharge rate
Inverter configuration

Therefore, battery sizing should use the manufacturer's usable-capacity information rather than assuming the entire nameplate capacity is always available.

DEPTH OF DISCHARGE

Depth of discharge, commonly abbreviated as DoD, describes how much of the battery's capacity has been used.

If a 10kWh battery is discharged by 80%, approximately 8kWh has been taken from its rated energy capacity.

If the system is configured to use only 90%, approximately 9kWh may be available.

The permitted value depends on the battery technology and manufacturer.

Repeatedly using a battery outside its recommended operating limits can affect performance and lifespan.

LITHIUM BATTERIES

Lithium batteries are widely used in modern residential and commercial solar systems.

Lithium iron phosphate, commonly called LiFePO4 or LFP, is particularly popular for stationary energy storage.

Advantages can include:

High usable capacity
Long cycle life
Good efficiency
Low maintenance
Consistent performance
High depth-of-discharge capability
Battery-management systems

The exact characteristics vary by manufacturer.

LEAD-ACID BATTERIES

Lead-acid batteries have also been used extensively in solar installations.

They can include:

AGM
Gel
Flooded lead-acid
Other lead-acid technologies

Their operating characteristics differ from lithium batteries.

In many applications, lead-acid systems are designed around more conservative discharge levels to support battery longevity.

This means a battery with the same nameplate kWh may not provide the same practical usable energy as a modern lithium system.

BATTERY EFFICIENCY

Energy is lost during charging and discharging.

For example, energy generated by solar panels may pass through:

PV array → charge electronics → battery → inverter → AC loads.

Each stage can introduce losses.

The battery also has its own round-trip efficiency.

Therefore, calculating backup time by simply dividing nameplate kWh by load power can overestimate real-world runtime.

A professional calculation should include appropriate efficiency assumptions.

INVERTER EFFICIENCY

The inverter converts DC energy from the battery into AC electricity for household appliances.

This conversion is not perfectly efficient.

For example, if the loads require a certain amount of AC energy, the battery may need to provide more DC energy because some energy is lost during conversion.

Inverter standby consumption can also contribute to energy usage.

This becomes particularly noticeable during long outages.

STANDBY LOAD

The inverter itself consumes some energy even when household loads are relatively small.

There may also be continuous consumption from:

Wi-Fi routers
CCTV
Security systems
Network switches
Chargers
Control systems
Refrigeration controls
Monitoring devices

Small loads can accumulate over many hours.

This is why a battery may discharge overnight even when the homeowner believes very few appliances were operating.

5KWH BATTERY BACKUP

Consider a 5kWh battery.

If approximately 4kWh is practically usable after considering system settings and losses, then:

At 500W average load:

4kWh ÷ 0.5kW = approximately 8 hours.

At 1kW:

4kWh ÷ 1kW = approximately 4 hours.

At 2kW:

4kWh ÷ 2kW = approximately 2 hours.

These are illustrative calculations rather than guarantees.

10KWH BATTERY BACKUP

Consider a 10kWh battery.

Suppose approximately 8kWh is practically available for the intended operating range.

At 500W average load:

8 ÷ 0.5 = approximately 16 hours.

At 1kW:

8 ÷ 1 = approximately 8 hours.

At 2kW:

8 ÷ 2 = approximately 4 hours.

At 4kW:

8 ÷ 4 = approximately 2 hours.

Again, actual runtime depends on the battery and inverter configuration.

15KWH BATTERY BACKUP

A 15kWh battery provides more stored energy and can support longer outages.

Suppose approximately 12kWh is available for practical use.

At a 1kW average load:

12 ÷ 1 = approximately 12 hours.

At 2kW:

12 ÷ 2 = approximately 6 hours.

At 3kW:

12 ÷ 3 = approximately 4 hours.

At 5kW:

12 ÷ 5 = approximately 2.4 hours.

This illustrates why high-power loads can consume stored energy very quickly.

20KWH BATTERY BACKUP

A 20kWh battery can provide substantial backup energy for a properly designed home or business.

If approximately 16kWh is available:

At 1kW average consumption:

16 hours.

At 2kW:

8 hours.

At 4kW:

4 hours.

At 5kW:

3.2 hours.

A larger battery does not eliminate the need for load management.

WHAT CAN A 10KWH BATTERY RUN?

This depends on the appliances.

A 10kWh battery could potentially support essential loads such as:

LED lighting
Television
Wi-Fi
CCTV
Refrigerator
Freezer
Computers
Phone chargers
Security systems

for a substantial period.

However, adding high-energy appliances changes the calculation.

For example:

Electric kettle
Iron
Electric oven
Electric cooker
Water heater
Air conditioner

can significantly increase instantaneous and daily energy consumption.

REFRIGERATOR BACKUP

A refrigerator does not normally consume its maximum rated power continuously.

The compressor cycles on and off.

Therefore, its average energy consumption is generally lower than simply multiplying its compressor wattage by 24 hours.

However, the inverter must still handle compressor starting requirements.

A properly configured solar system can keep refrigeration operating during a grid outage without necessarily consuming excessive battery energy.

TELEVISION BACKUP

Televisions are generally moderate loads compared with electric heating appliances.

Suppose a television and associated entertainment equipment consume approximately 150W.

Running for five hours would use roughly:

0.15kW × 5 = 0.75kWh.

Additional inverter losses would need to be considered.

This is relatively small compared with a high-power electric heater.

LIGHTING BACKUP

LED lighting is one of the easiest loads to support with a battery.

Suppose ten LED lamps average 10W each.

Total lighting load:

10 × 10W = 100W.

If they operate for five hours:

0.1kW × 5 = 0.5kWh.

Efficient lighting can therefore provide long backup periods.

WIFI AND INTERNET

A Wi-Fi router may use relatively little power but can operate continuously.

During a long outage, the router's energy consumption becomes relevant.

Internet equipment can often be included in an essential-load backup circuit.

CCTV BACKUP

CCTV systems can operate continuously.

The system may include:

Cameras
DVR/NVR
Monitor
Network equipment
PoE equipment

Although individual devices may consume modest amounts of power, continuous operation over many hours adds to battery consumption.

Security equipment is often prioritized during backup design.

COMPUTERS

Desktop computers can consume more power than laptops.

A computer workstation may include:

Desktop PC
Monitor
Printer
Network equipment
Speakers

A laptop generally has lower average energy consumption because it contains its own battery.

For offices, load calculations should consider the number of computers operating simultaneously.

WASHING MACHINE

A washing machine's energy use depends heavily on the selected cycle.

A cold-water cycle may use considerably less electricity than a cycle involving water heating.

The motor and pump also produce varying loads.

If a washing machine is connected to a battery backup system, the inverter should have sufficient capacity to handle its instantaneous load.

MICROWAVE

A microwave can have a relatively high instantaneous power rating.

For example, a microwave may consume around 1kW or more from the electrical supply depending on its model.

However, it usually operates for short periods.

A 1.2kW microwave running for five minutes consumes approximately:

1.2 × 5/60 = 0.1kWh.

Therefore, high power does not always mean high daily energy consumption.

Both power and duration matter.

ELECTRIC KETTLE

An electric kettle can have a high power rating but normally runs for only a few minutes.

A 2kW kettle operating for ten minutes uses:

2 × 10/60 = approximately 0.33kWh.

Several boiling cycles per day can add up.

During an outage, reducing unnecessary kettle use can extend battery runtime.

ELECTRIC IRON

An iron can also have a relatively high power rating.

If an iron averages approximately 1.5kW and is used for one hour:

1.5 × 1 = 1.5kWh.

That can consume a significant portion of a small battery.

ELECTRIC COOKER

Electric cooking can dramatically affect battery runtime.

A single cooking element may consume substantial power.

An oven can consume even more.

Using several cooking zones simultaneously can push a household close to or beyond the inverter's output limit.

A battery system designed primarily for lighting, refrigeration and electronics may therefore not be suitable for unrestricted electric cooking during an outage.

ELECTRIC WATER HEATER

Electric water heaters are among the most demanding household loads.

A typical electric water heater can consume several kilowatts.

Running one from a battery can drain stored energy quickly.

For example, if a 3kW heater operates for two hours:

3kW × 2 hours = 6kWh.

That is a substantial amount of energy from a household battery.

AIR CONDITIONER

Air conditioning can also consume significant energy.

A 1.5kW average air-conditioning load operating for five hours would use:

1.5 × 5 = 7.5kWh.

That could consume most of the usable capacity of a modest battery.

If multiple air conditioners operate simultaneously, the energy requirement increases considerably.

PUMPS

Water pumps can create both energy and starting-load considerations.

A pump might have a moderate running power but require higher starting power.

The inverter therefore needs appropriate surge capability.

Long pump operation can also consume substantial battery energy.

For borehole systems, specialized solar-pumping designs may be more appropriate than treating the pump like an ordinary household appliance.

ESSENTIAL LOADS

One of the best ways to extend battery backup is to separate essential loads from non-essential loads.

Essential loads may include:

Lighting
Refrigerator
Wi-Fi
CCTV
Security systems
Selected sockets
Television
Medical or critical equipment where appropriately designed

Non-essential loads may include:

Electric oven
Water heater
Heavy cooking appliances
Large air conditioners
High-power workshop equipment

The exact selection should be determined by the customer's requirements.

ESSENTIAL LOADS BOARD

A hybrid solar installation can be designed with a dedicated essential-load distribution board.

When the grid fails, the inverter supplies the designated circuits.

This prevents unnecessary appliances from consuming battery energy.

For example, the essential-load board might supply:

Living-room lighting
Bedrooms
Refrigerator
Wi-Fi
CCTV
Television
Selected sockets

The electric cooker and water heater may remain outside the backup circuit.

This can significantly extend runtime.

WHOLE-HOUSE BACKUP

Whole-house backup is possible with appropriately sized equipment.

But a whole-house system should be designed around the home's maximum demand and daily energy consumption.

If the property uses:

Multiple air conditioners
Electric cooking
Electric water heating
Pumps
Refrigeration
Large appliances

the battery and inverter requirements can become much larger than those of a basic essential-load system.

5KW INVERTER WITH 10KWH BATTERY

A common residential configuration might use:

5kW hybrid inverter

plus:

10kWh lithium battery

plus:

5–6kW PV array, where permitted by the inverter.

This can be a useful configuration for a medium-sized home.

But the actual backup duration depends on the load.

At approximately 1kW average consumption, the battery could potentially provide many hours.

At approximately 4kW average consumption, runtime would be much shorter.

5KW INVERTER WITH 15KWH BATTERY

A 15kWh battery provides greater energy storage.

This can be useful for households requiring longer backup.

It can also reduce the frequency of deep battery discharge during ordinary outages.

However, the inverter's battery charging and discharging specifications must be compatible with the battery system.

5KW INVERTER WITH 20KWH BATTERY

A 20kWh battery may be appropriate for larger backup requirements.

But increasing battery capacity does not automatically solve every problem.

The PV array must be able to recharge the battery adequately.

The inverter must support the battery configuration.

The battery must have appropriate communication and protection.

The installation must also provide suitable space and ventilation according to the equipment requirements.

SOLAR PANELS DURING AN OUTAGE

One major advantage of a solar-plus-battery system is that solar panels can continue producing electricity during a grid outage when the system is properly configured.

The solar energy can:

Supply active loads
Charge the battery
Reduce battery discharge
Extend backup duration

This means battery runtime does not necessarily equal total outage duration.

If sunlight is available, solar generation can replenish some of the energy being consumed.

CLOUDY WEATHER

Clouds can reduce solar production.

A system should therefore not be designed under the assumption that the panels will always deliver their maximum rated power.

During cloudy conditions, battery discharge may increase.

An appropriately sized battery provides a buffer.

NIGHTTIME OUTAGES

A nighttime outage presents a different situation.

The solar panels are not producing useful energy after sunset.

The battery therefore becomes the primary backup source.

This is why battery capacity should be based on the expected nighttime load and desired backup duration.

DAYTIME OUTAGES

During daytime outages, solar panels can contribute energy.

Suppose a home has:

6kW PV array
5kW hybrid inverter
10kWh battery

During good sunlight, the PV array may supply the loads and potentially charge the battery, subject to system limitations.

This can substantially extend the duration of a grid outage.

BATTERY AGE

Battery performance changes with age.

As batteries undergo charging and discharging cycles, their available capacity can gradually decline.

Therefore, a battery that initially provides a certain backup duration may eventually provide somewhat less.

Proper charging, appropriate operating temperatures and adherence to manufacturer recommendations can help preserve performance.

BATTERY TEMPERATURE

Temperature affects battery performance.

The battery installation location should comply with the manufacturer's requirements.

Extreme temperatures can affect:

Capacity
Charging
Discharging
Battery lifespan
Safety

Battery equipment should not simply be placed anywhere convenient.

BATTERY MANAGEMENT SYSTEM

Lithium batteries normally use a Battery Management System, or BMS.

The BMS helps monitor and manage:

Cell voltage
Battery temperature
Charging
Discharging
Protection conditions
Cell balancing
Communication

A compatible inverter-battery communication setup can improve system management.

BATTERY COMMUNICATION

Some hybrid inverters communicate with lithium batteries using protocols supported by both manufacturers.

Correct communication can allow the inverter to receive information such as:

State of charge
Maximum charging current
Maximum discharge current
Battery alarms
Temperature
Protection status

Incorrect settings or incompatible communication can cause charging or backup problems.

BATTERY VOLTAGE

Solar batteries are available in different system voltages.

A 5kW inverter might use a high-voltage battery architecture or a low-voltage battery architecture depending on the manufacturer.

The battery voltage affects current.

For example, delivering 5kW from a lower-voltage DC system requires higher current than delivering the same power from a higher-voltage battery system.

This affects:

Cable size
Protection
Connectors
Battery configuration
Heat generation

BATTERY CABLES AND PROTECTION

Battery cables must be appropriately sized.

Poor connections can cause:

Voltage drop
Heating
Reduced inverter performance
Energy losses
Safety hazards

Battery protection should be designed according to the battery and inverter specifications.

LOAD MANAGEMENT

Load management is one of the most effective ways to extend backup.

During an outage, consider prioritizing:

Lighting
Refrigeration
Security
Internet
Communication
Essential electronics

Avoid unnecessary simultaneous use of:

Electric heaters
Electric ovens
Water heaters
Irons
Kettles
High-power pumps

unless the system was specifically designed to support them.

BATTERY BACKUP AND ELECTRIC COOKING

A customer may have a 10kWh battery and assume that the battery can comfortably run the entire kitchen.

This may not be true.

A kettle, oven, cooker and microwave can create a large instantaneous load.

If several operate simultaneously, they can approach the inverter's output limit.

Even if the inverter can handle the power, the battery may discharge rapidly.

BATTERY BACKUP AND FRIDGES

Refrigerators are usually a more manageable backup load.

However, large commercial freezers and multiple refrigeration systems can consume significant energy.

For restaurants, supermarkets, butcheries and cold-storage facilities, battery sizing should be based on actual refrigeration energy consumption.

COMMERCIAL BACKUP

Businesses have different requirements from homes.

An office may prioritize:

Computers
Servers
Internet
Security
Lighting

A shop may prioritize:

Refrigeration
POS
Lighting
Security

A restaurant may require:

Refrigeration
POS
Lighting
Internet
Security
Selected kitchen equipment

An industrial workshop may have motors and machines requiring much higher power.

The battery should therefore be sized around the business's critical loads.

GENERATOR INTEGRATION

Some larger solar systems combine:

Solar
Battery
Grid
Generator

A generator can provide backup when the battery becomes low or when solar generation is insufficient.

Hybrid systems can be configured to coordinate these sources depending on the equipment.

This can be useful for businesses requiring high reliability.

BATTERY BACKUP FOR SECURITY

Security systems are often excellent candidates for battery backup.

These may include:

CCTV
Electric fence systems
Alarm systems
Access control
Gate motors
Security lighting
Network equipment

Keeping security systems active during outages can be an important design objective.

BATTERY BACKUP FOR INTERNET

For businesses and homes dependent on internet connectivity, keeping routers and network equipment operational during outages can be valuable.

The energy requirement is usually modest compared with heating or cooking appliances.

This makes internet equipment a practical essential load.

BATTERY BACKUP FOR HOME OFFICE

A home office may need:

Laptop
Monitor
Router
Printer
Lighting
Phone charging

These loads can generally be supported efficiently by a properly sized backup system.

HOW TO ESTIMATE YOUR OWN BACKUP TIME

Start by listing the appliances you want operating during an outage.

Record:

Appliance name
Power rating
Number of units
Hours of operation
Expected daily use

Then calculate energy.

For example:

A 100W device running for five hours:

0.1kW × 5 = 0.5kWh.

A 500W device running for four hours:

0.5kW × 4 = 2kWh.

A 2kW device running for one hour:

2kW × 1 = 2kWh.

Add the energy requirements of the appliances.

Then compare the total with the battery's usable energy.

EXAMPLE HOME BACKUP TABLE

Consider a simplified outage load:

Appliance	Approx. Average Power	Runtime	Approx. Energy
Lighting	150W	6 hours	0.9kWh
Refrigerator	150W average	10 hours	1.5kWh
Wi-Fi	15W	10 hours	0.15kWh
CCTV	40W	10 hours	0.4kWh
Television	120W	5 hours	0.6kWh
Laptop/computer	100W	5 hours	0.5kWh

Approximate load energy:

4.05kWh

A suitably sized battery with sufficient usable capacity could therefore support these loads for the specified period, subject to inverter and battery losses.

WHY ACTUAL LOADS ARE BETTER THAN ESTIMATES

Appliance labels are not always representative of actual energy consumption.

For better sizing, energy can be measured using:

Energy meters
Smart-meter information
Monitoring systems
Clamp meters
Appliance energy monitors

Historical electricity consumption can also provide useful information.

ELECTRICITY BILLS

Monthly electricity bills can help estimate total consumption.

However, the bill alone may not show when energy is consumed.

Two homes can have the same monthly energy consumption but completely different load profiles.

One may consume most electricity during the day.

Another may consume most electricity at night.

This difference affects solar and battery sizing.

DAYTIME LOADS

If much of the home's energy consumption occurs during daylight hours, a larger PV array can directly supply those loads.

This can reduce the amount of energy that needs to pass through the battery.

That may improve overall system efficiency.

NIGHTTIME LOADS

If the majority of energy is consumed after sunset, battery capacity becomes more important.

For example:

Television
Lighting
Cooking
Security
Refrigeration
Internet

may continue operating after sunset.

The battery needs enough usable energy to support the required nighttime load.

BATTERY SIZING FOR OVERNIGHT BACKUP

Suppose essential nighttime consumption is estimated at 6kWh.

A battery system may need more than 6kWh of nameplate capacity because of:

Usable-capacity limits
Depth-of-discharge settings
Inverter losses
Battery losses
Reserve capacity

The actual battery size should therefore be selected using a complete system calculation.

RESERVE CAPACITY

Some installations deliberately retain a reserve.

For example, the system may avoid completely discharging the battery so that energy remains available for an unexpected outage or emergency.

Reserve settings can be configured according to system requirements.

BACKUP DURATION IS NOT ALWAYS THE MAIN GOAL

A homeowner might say:

"I want 24 hours of backup."

That sounds straightforward, but the actual requirement needs clarification.

Does 24 hours mean:

The entire house operating normally?
Only essential loads?
Refrigeration and security?
Nighttime loads?
Including electric cooking?
Including air conditioning?
Including water heating?

The energy requirement can vary enormously.

24-HOUR BACKUP

Suppose essential loads average only 500W.

Over 24 hours:

0.5kW × 24 = 12kWh.

After considering losses and reserve capacity, the battery may need to be larger than 12kWh.

But if the average load is 2kW:

2kW × 24 = 48kWh.

That is a completely different battery system.

This demonstrates why backup duration cannot be specified without defining the load.

48-HOUR BACKUP

For long outages, battery sizing becomes increasingly important.

A 48-hour backup system may need:

Large battery capacity
Adequate PV generation
Efficient appliances
Load prioritization
Generator integration in some applications

For critical commercial facilities, redundancy may also be considered.

MULTI-DAY OUTAGES

Where prolonged outages are possible, a solar-plus-battery system should not rely exclusively on one night's stored energy.

The PV array should have sufficient capacity to recharge the battery while supporting daytime loads.

Weather conditions should also be considered.

SOLAR RECHARGING

Suppose the battery has been partially discharged overnight.

The following day, solar energy can:

Supply active loads.
Recharge the battery.
Restore backup capacity.

If the PV array is too small relative to daily consumption, the battery may remain partially discharged.

Repeatedly operating this way can affect system reliability.

BATTERY AND SOLAR BALANCE

A large battery paired with a very small PV array can take a long time to recharge.

A large PV array paired with a small battery may produce substantial daytime energy but have limited nighttime storage.

The system should therefore balance:

PV capacity
Battery capacity
Inverter capacity
Daily energy demand
Backup requirement

BATTERY CHARGING POWER

The battery also has maximum charging-current and charging-power limits.

A very large solar array does not mean the battery can accept unlimited charging power.

The inverter and battery specifications determine how quickly energy can be stored.

BATTERY DISCHARGE POWER

Similarly, a large battery may not necessarily deliver unlimited power.

The battery's maximum discharge current and power must be considered.

For example, a large battery with a limited discharge rating may not be suitable for very high instantaneous loads.

The inverter must also be able to deliver the required AC power.

INVERTER SURGE CAPACITY

Some appliances require high starting power.

Examples include:

Pumps
Refrigerators
Freezers
Compressors
Motors
Some air conditioners

The inverter should have adequate surge capability for the intended loads.

POWER FACTOR

Motor-driven equipment can have power-factor characteristics that affect the electrical system.

Commercial and industrial installations should therefore be evaluated using actual electrical measurements where appropriate.

This is especially important for:

Pumps
Compressors
Motors
Workshops
Refrigeration
Industrial equipment

MONITORING BATTERY BACKUP

A good solar system should allow the owner to monitor battery state of charge.

Useful information may include:

Battery percentage
Voltage
Current
Charging power
Discharging power
Solar generation
Load consumption
Grid status
Historical performance

Monitoring allows the homeowner to understand how quickly the battery is being depleted.

WHY A BATTERY MAY DIE FASTER THAN EXPECTED

If a customer expects ten hours but receives only four, possible causes include:

Higher-than-expected loads
Incorrect battery capacity assumptions
Battery degradation
High inverter consumption
Incorrect battery settings
Excessive discharge
Poor battery condition
Temperature
Faulty equipment
Hidden loads
High standby consumption

The system should be measured rather than assuming the battery is defective.

BATTERY TROUBLESHOOTING

A technician can investigate:

Battery state of health
Voltage
Current
BMS information
Inverter settings
Load profile
Charging behavior
Discharge behavior
Temperature
Cable connections
Protection devices

This helps determine whether the problem is the battery or another part of the system.

REPLACING AN OLD BATTERY

When replacing a battery, do not select capacity based solely on the old battery's label.

The household's energy requirements may have changed.

For example, the owner may now have:

Additional refrigerators
More computers
Electric cooking
Air conditioning
Additional rooms
Larger pumps

The replacement system should therefore be reassessed.

EXPANDING BATTERY CAPACITY

Many modular lithium battery systems allow expansion.

Additional modules may increase stored energy.

However, expansion must comply with the manufacturer's requirements.

The inverter must support the increased battery capacity and charging/discharging current.

Battery modules may also need to meet requirements concerning:

Age
Model
Firmware
State of charge
Configuration
Communication

EXPANDING SOLAR PANELS

If battery capacity is increased, the PV array may also need expansion.

Otherwise, the larger battery could take longer to recharge.

The inverter's maximum PV input must be checked before adding additional panels.

SOLAR SYSTEM FOR LONG OUTAGES

If a property regularly experiences long outages, the ideal system may include:

Adequate PV
Sufficient battery storage
Hybrid inverter
Essential-load distribution
Monitoring
Generator backup where required

This provides more resilience than simply installing a small battery.

MAINTAINING BATTERY PERFORMANCE

Battery maintenance depends on the technology.

For lithium systems:

Monitor temperature.
Maintain appropriate settings.
Keep communication healthy.
Follow manufacturer recommendations.
Keep terminals and cables in good condition.
Avoid unauthorized modifications.

For lead-acid systems:

Follow the manufacturer's charging requirements.
Maintain appropriate ventilation where required.
Inspect terminals.
Monitor electrolyte where applicable.
Avoid excessive discharge.

BATTERY SAFETY

Battery systems can contain significant stored energy.

Do not open battery enclosures or modify internal components without appropriate technical competence.

Do not bypass the BMS.

Do not use damaged batteries.

Do not connect incompatible batteries.

Do not place batteries in locations prohibited by the manufacturer.

CHOOSING THE RIGHT BATTERY SIZE

The right battery size should be based on:

Required backup energy

plus appropriate allowances for:

Usable capacity
Efficiency
Reserve
Battery aging
Operating limits

A professional designer can convert the customer's desired backup duration into a suitable battery capacity.

A SIMPLE FORMULA

A useful conceptual formula is:

Required battery capacity ≈ Daily backup energy ÷ allowable usable fraction ÷ system efficiency

For example, if essential loads require 8kWh and the design allows approximately 80% usable capacity with additional system losses, the nameplate battery requirement will be greater than 8kWh.

The exact calculation should use the actual battery manufacturer's specifications.