Why Your Solar Battery Is Not Lasting as Long as It Should — 12 Things Every Installer Should Check

One of the calls I know almost every solar installer has received is:

“Engineer, this battery is not lasting.”

Sometimes the customer calls at 11pm.

Sometimes it is 2am.

Sometimes they call the next morning and say:

“You told me this battery would last all night. It went off before morning.”

At that point, the easiest thing to do is blame the battery.

But I don’t like troubleshooting that way.

A battery can be perfectly healthy and still fail to deliver the backup time the customer expected.

The problem could be the load.

It could be the original system sizing.

It could be the inverter settings.

It could be the battery’s usable capacity.

It could be excessive discharge current.

It could be poor cabling.

It could even be that the customer is using more appliances than they told you during the initial assessment.

So when a customer tells me, “The battery isn’t lasting,” I don’t immediately condemn the battery.

I start investigating.

Here are 12 things I would check.

1. Go back to the original load calculation

This is the first place I would look.

Before touching the battery, I want to know what the system was actually designed to carry.

What appliances were included?

What was their estimated power consumption?

How many hours of operation were assumed?

Which appliances were expected to run simultaneously?

What backup duration was promised?

This is where proper solar sizing becomes important.

If the customer was originally calculated to use 3kWh overnight but is actually consuming 6kWh, the battery may not be the problem.

The system was simply designed around a lower energy requirement.

The Globisun Solar App can help installers and customers work through appliance loads and energy requirements before committing to a system.

Download the Globisun Solar App for solar sizing

It doesn’t replace professional engineering judgement, but it is useful for getting a clearer picture of the customer’s requirement.

2. Check what the customer is actually running

This is where things can get interesting.

A customer may tell you:

“Nothing much was running.”

Then you look at the inverter history and discover:

• Two air conditioners
• Freezer
• Refrigerator
• Television
• Fans
• Water pump
• Decoder
• Router
• Several lights

were all running during the period.

The system may have been doing exactly what it was asked to do.

Customers don’t always realise how much energy some appliances consume.

And sometimes their usage changes after installation.

A customer may initially tell you:

“I only want the AC occasionally.”

Three months later, the AC is running every night.

That changes the battery requirement considerably.

3. Don’t confuse battery capacity with inverter capacity

This mistake causes a lot of misunderstanding.

A 10kVA inverter doesn’t mean you have 10kWh of stored energy.

Likewise, a 10kWh battery doesn’t mean you can automatically run a 10kW load for one hour.

kVA and kWh describe different things.

The inverter is concerned primarily with power delivery.

The battery stores energy.

So when a customer says:

“But I bought a 10kVA inverter. Why isn’t the battery lasting?”

I explain that the inverter’s capacity doesn’t determine the battery’s runtime.

The load and available battery energy determine how long the system can operate.

4. Calculate usable battery energy, not just the nameplate capacity

Suppose a battery is advertised as having a particular kWh capacity.

That doesn’t mean every bit of that energy should be treated as available to the AC loads.

There are operating limits and system losses.

For lithium batteries, the manufacturer’s specified operating limits and BMS behaviour also matter.

Then you have inverter conversion losses and other losses between the battery and the appliances.

So when calculating expected runtime, I don’t simply take the battery’s advertised capacity and divide it by the load.

I account for the energy that can realistically be delivered.

This is one reason two systems with batteries carrying similar headline capacities can produce different real-world backup times.

5. Check the battery’s state of charge

Before concluding that a battery is bad, check what is actually happening to its state of charge.

Don’t rely only on the percentage displayed on a screen.

Depending on the battery and inverter, the displayed state of charge can be based on different measurement methods or battery communication data.

For lithium systems, I also want to know what the BMS is reporting.

If the battery suddenly drops from a seemingly comfortable state of charge to a low state under load, I want to investigate why.

It could be:

• Voltage sag
• High discharge current
• BMS behaviour
• Cell imbalance
• Communication problems
• Incorrect configuration
• Actual low state of charge

The displayed percentage is a clue.

It isn’t the entire diagnosis.

6. Check the battery discharge current

This is especially important on high-power systems.

Remember that power is related to voltage and current.

At a lower battery voltage, supplying a high load can require a very high DC current.

For example, a system delivering several kilowatts from a 48V battery bank can draw a substantial current.

If the battery, BMS, cables or connections aren’t designed for that demand, problems can occur.

The battery may limit output.

The voltage may sag.

The BMS may intervene.

The inverter may shut down.

And the customer may conclude:

“The battery doesn’t last.”

Sometimes the battery isn’t failing.

The system is simply demanding more current than the battery arrangement is designed to comfortably provide.

7. Check the inverter’s battery settings

I never like changing battery settings blindly.

The inverter needs to be configured according to the battery manufacturer’s recommendations and the actual battery chemistry.

Depending on the system, settings can include:

• Charging parameters
• Low-voltage protection
• Maximum charging current
• Maximum discharge current
• Battery type
• Cut-off thresholds
• Communication settings
• BMS-related settings

If these settings are wrong, the inverter may stop drawing from the battery earlier than expected.

Or the battery may not be charged correctly.

Or the BMS may repeatedly intervene.

If the battery manufacturer provides recommended settings for the inverter, that’s where I start.

Not from a random WhatsApp group.

Not from what somebody used on another battery.

And certainly not from guessing.

8. Check lithium BMS communication

With compatible lithium systems, communication between the battery BMS and inverter can be extremely important.

If the communication cable, protocol, battery address, inverter configuration or firmware compatibility is wrong, the system may not behave as expected.

I’ve seen situations where the battery itself was healthy but the inverter wasn’t receiving the correct information.

So if a lithium battery isn’t behaving normally, I check:

Is communication established?

Is the inverter recognising the battery correctly?

Is the correct battery protocol selected?

Are the BMS limits being reported?

Are there any BMS alarms?

Don’t assume that because the battery is powered on, communication is working correctly.

9. Check the battery cables and connections

This is one of those things that can be overlooked because it looks too simple.

But I take it seriously.

Check:

• Cable size
• Cable length
• Terminations
• Lug quality
• Torque
• Loose connections
• Corrosion
• Heat at terminals
• Voltage drop

A poor connection can create resistance and heat.

A cable that is inadequate for the current can create unnecessary losses and voltage drop.

On a high-current battery system, these aren’t minor details.

The battery may be perfectly healthy, but the energy isn’t being transferred efficiently to the inverter.

10. Check whether the batteries are properly configured in parallel

If multiple batteries are connected together, don’t just look at the total kWh.

Look at how they are connected.

Are the batteries compatible?

Are they the same model?

Are they of similar age and condition?

Are the cables properly arranged?

Are the batteries sharing current appropriately?

Is the manufacturer’s recommended parallel configuration being followed?

Are communication requirements being satisfied?

Poorly configured parallel batteries can create imbalance.

One battery may work harder than another.

That can affect performance and battery life.

When I see multiple batteries, I don’t just say:

“That’s 20kWh.”

I want to understand how that 20kWh bank has actually been constructed.

11. Check the temperature and installation environment

Nigeria’s environment can be unforgiving.

Heat matters.

A battery installed in a poorly ventilated location can operate under conditions that aren’t ideal.

The same applies to the inverter.

I check where the equipment is installed.

Is the battery exposed to excessive heat?

Is the inverter installed in a cramped space?

Is there enough ventilation?

Is the equipment sitting in direct sunlight?

Is dust accumulating around the installation?

Environmental conditions can affect equipment performance and longevity.

A battery room shouldn’t simply be treated as a place where we put the battery because there is an empty corner.

The installation environment is part of the design.

12. Check whether the battery is actually receiving enough energy from solar

This is another situation where installers sometimes blame the battery unnecessarily.

Suppose the customer uses a significant amount of energy every night.

The battery reaches a low state of charge.

Then during the day, the solar array isn’t producing enough energy to properly recharge it.

The next night begins with a battery that isn’t fully recovered.

The customer uses it again.

The same thing happens the following day.

Eventually the customer says:

“This battery doesn’t last.”

But the real problem may be insufficient PV generation.

So I check:

• PV array capacity
• Actual daytime production
• Shading
• Panel cleanliness
• PV string configuration
• MPPT operation
• PV voltage
• PV current
• Weather conditions
• Customer daytime consumption
• Battery charging current

A battery cannot magically replace energy that the solar array isn’t putting back into the system.

The calculation I use to think about backup time

At its simplest, the principle is straightforward:

Backup time depends on available usable battery energy and the load being supplied.

If the load increases, runtime decreases.

If the usable battery energy increases, runtime generally increases.

But in a real installation, we also have to account for losses, battery operating limits, inverter efficiency and the behaviour of the actual equipment.

This is why I don’t like giving customers a blanket statement such as:

“This battery will last exactly 10 hours.”

The better statement is:

“Under this expected load and these operating assumptions, we expect approximately this much runtime.”

That’s a much more honest way to communicate.

What if the battery is genuinely faulty?

Yes, batteries can fail.

I’m not saying every battery complaint is caused by poor sizing or customer behaviour.

A battery can have:

• Cell problems
• BMS faults
• Internal degradation
• Manufacturing defects
• Communication faults
• Excessive internal resistance
• Capacity loss

But I want evidence before declaring it faulty.

If the system is underperforming, I investigate the entire chain.

Load → inverter → cables → battery → BMS → PV → settings → environment.

That gives me a much better chance of finding the actual cause.

Don’t replace the battery before finding the problem

This is one of the most expensive mistakes an installer can make.

Imagine a customer has a perfectly healthy battery but is running an additional 2kW load that wasn’t included in the original design.

You replace the battery.

The customer runs the same load.

The new battery also doesn’t last.

Now the customer has spent money on a replacement without solving the problem.

Or perhaps the battery isn’t being fully charged because of insufficient PV.

Again, replacing the battery doesn’t solve the underlying problem.

Before recommending a replacement, find out why the existing system isn’t delivering the expected result.

What I would do when a customer calls

If someone calls me and says:

“The battery isn’t lasting.”

I would start asking questions.

What appliances were running?

What time did the battery start?

What was the battery state of charge?

What load was the inverter showing?

What time did the battery shut down?

What error or warning appeared?

Was there solar input during the day?

Was the battery fully charged before the outage?

Has anything changed in the customer’s usage?

Then I would inspect the system.

If the inverter has historical data, I use it.

If the battery has monitoring, I use it.

If measurements are required, I take them.

I don’t want to troubleshoot from assumptions.

A useful test: reduce the load

One simple way of understanding a runtime complaint is to observe what happens when the load is reduced.

Suppose the customer normally runs:

• Two ACs
• TV
• Fans
• Refrigerator
• Freezer
• Lights

and the battery doesn’t last.

Turn off the high-energy loads and observe the system under a significantly lower load.

If runtime improves dramatically, that tells you something.

It doesn’t automatically mean the battery is perfect, but it points you towards the load and energy requirement.

Troubleshooting should be about gathering evidence.

The customer may need education, not a new battery

Sometimes the system is performing exactly as designed.

The customer simply doesn’t understand the relationship between load and runtime.

A customer may think:

“I bought a 10kWh battery, so I should be able to use everything in the house all night.”

That’s not necessarily realistic.

If the customer wants longer backup, there are several possible solutions:

• Reduce the load
• Increase usable battery capacity
• Increase PV generation
• Improve system efficiency
• Change usage patterns
• Upgrade the inverter if necessary

The correct solution depends on what the investigation reveals.

Use the Globisun Solar App before and after installation

For installers, one of the useful habits is to establish the customer’s expected load and energy requirement before equipment is purchased.

The Globisun Solar App can help with that process.

Get the Globisun Solar App

Use it to help work through the customer’s appliances and solar sizing requirements.

Then, after installation, compare the customer’s actual usage with the original assumptions.

If the customer is consistently consuming much more energy than the original design allowed for, you’ve got useful evidence.

That is much better than simply saying:

“The battery is bad.”

Final thought

A battery that isn’t lasting is not automatically a bad battery.

Sometimes the battery is undersized.

Sometimes the load is higher than expected.

Sometimes the battery isn’t fully charging.

Sometimes the inverter settings are wrong.

Sometimes the cables or connections are poor.

Sometimes the BMS is limiting the battery.

Sometimes the PV system isn’t producing enough energy.

And sometimes, yes, the battery itself is faulty.

The job of a good installer is to find out which one it is.

I’ve learned that troubleshooting becomes much easier when I stop looking for someone to blame and start looking for evidence.

When a customer says:

“My battery isn’t lasting.”

Don’t immediately say:

“Buy another battery.”

Go back to the numbers.

Check the load.

Check the battery.

Check the inverter.

Check the PV.

Check the settings.

Check the cables.

Check the environment.

Then make your recommendation.

A good installer doesn’t just install a battery. He understands why that battery should last as long as it does — and can explain what happens when the customer’s actual usage changes.