How Do I Know If the Battery Capacity on a Solar Quote Is Correct?

Last reviewed: September 25, 2026

A battery line on a solar quotation is only useful when it tells you enough to calculate the energy you will actually receive. “One 200Ah battery”, “10kWh lithium battery” or “large battery bank” is not enough by itself.

To check whether the quoted capacity is reasonable, start with the appliances you want to run and the number of backup hours you need. Then check the battery’s chemistry, voltage, capacity, quantity, usable-energy assumption, discharge rating and compatibility with the inverter. A quote is not correct simply because the battery has a large Ah or kWh number.

Quick answer: calculate your backup energy first, then compare it with the battery’s usable energy after the recommended depth of discharge and inverter losses. For lithium, use kWh as the main capacity figure. For tubular, GEL and AGM batteries, check Ah together with voltage, quantity and chemistry. Also confirm that the battery can safely supply the inverter and that the quoted battery bank matches the inverter’s battery voltage.

1. Start with the backup load, not the battery label

The battery should be sized from the work you expect it to do. Write down the appliances or circuits that should remain on when public power goes off in your home, shop, office or business.

For each appliance, record:

• Its actual running wattage, preferably from the nameplate or manufacturer’s specification.
• How many units will run at the same time.
• How many hours you want them to operate from the battery.
• Whether the appliance has a motor or compressor with a starting surge.

The first energy estimate is:

Running load × backup hours = energy needed at the appliance side

For example, suppose the critical loads in a Nigerian home are:

This does not mean that a battery labelled 3.6kWh will definitely provide 3.6kWh to the appliances. Some stored energy must remain unavailable to protect the battery, and the inverter and cables also use energy. The calculation is a starting point, not a guarantee of runtime.

If your load includes a freezer, water pump, air conditioner or several refrigerators, do not check energy capacity alone. The inverter and battery must also handle the starting demand.

You can use the SolarPriceNG Battery Calculator to estimate the storage needed from your appliances and desired backup period. Use the result as a planning starting point and then verify the exact product specification.

2. Read the battery capacity in the correct unit

Lithium batteries: start with kWh

For a lithium battery, kWh is normally the clearest primary capacity figure when it is provided by the manufacturer. A quote may say 5kWh, 10kWh or 15kWh.

Still, ask what the number means. Confirm whether it is:

• Nominal stored energy or usable energy.
• The capacity of one battery or the total bank.
• Based on the manufacturer’s recommended depth of discharge.
• Available at the discharge power your inverter requires.

A 10kWh label does not automatically mean that 10kWh will reach your appliances. The usable amount depends on the manufacturer’s limits, battery-management system, discharge rate, temperature, battery age and inverter efficiency.

Tubular, GEL and AGM batteries: check Ah and voltage together

Lead-acid batteries are commonly quoted in Ah, but Ah alone is incomplete. You need the battery voltage and the number of batteries.

The simple nominal-energy calculation is:

Voltage × Ah × number of batteries = nominal Wh

For example:

• One 12V 200Ah battery: 12 × 200 = 2,400Wh, or 2.4kWh nominal.
• Four identical 12V 200Ah batteries connected as a 48V bank: 12 × 200 × 4 = 9,600Wh, or 9.6kWh nominal.

The second bank has a 48V system voltage and 200Ah at the bank level. Do not describe it simply as “800Ah at 48V”; that would be a different configuration. Series and parallel connections change the voltage, capacity and current behaviour.

For a simple explanation of why the voltage matters, see What Does 100Ah, 200Ah and 300Ah Mean in a Solar Battery?

3. Convert nominal capacity into a realistic usable-energy estimate

The battery capacity on a quote is usually not the same as the energy you should plan to consume. A useful planning formula is:

Estimated AC energy = nominal battery energy × usable fraction × inverter efficiency

Use the actual manufacturer’s figures where they are available. If the quote does not state them, ask the installer to show the assumptions rather than treating the result as certain.

Worked example: lithium battery

Return to the example load of 3.6kWh at the appliance side. If a planning calculation uses 85% usable capacity and 92% inverter efficiency:

Required nominal storage = 3.6 ÷ (0.85 × 0.92) = about 4.60kWh

A quoted 5kWh lithium battery could therefore be a reasonable starting point for that simplified load and six-hour period. But it still needs to pass the inverter-voltage, continuous-discharge, peak-power and manufacturer-compatibility checks. If the refrigerator starts while other appliances are running, the inverter’s surge capability matters too.

Worked example: four 12V 200Ah tubular batteries

Four 12V 200Ah batteries connected for a 48V bank have approximately 9.6kWh nominal energy. If a planning assumption allows 50% usable battery energy and 82% inverter efficiency:

Estimated AC energy = 9.6 × 0.50 × 0.82 = about 3.94kWh

That is close to the 3.6kWh load example before allowing for additional variation. It does not mean the bank will always deliver 3.94kWh. Lead-acid capacity can change with discharge rate, age, temperature, maintenance and the manufacturer’s test conditions. A bank that is already old or repeatedly undercharged may deliver much less.

These examples show why “four batteries” or “200Ah battery” is not enough information. The chemistry, voltage, quantity and usable-energy assumption all affect the answer.

4. Check whether the battery can supply the inverter

A battery can have enough stored energy and still be unsuitable for the inverter. The battery must deliver the current required by the inverter at the planned load.

As a rough illustration, a 1,200W AC load on a 48V system at 92% inverter efficiency would require approximately:

1,200 ÷ (48 × 0.92) = about 27A

The actual current can be higher when the battery voltage falls, the load increases, the inverter is less efficient or a motor starts. Check the battery’s maximum continuous discharge current and peak or short-term discharge rating. For lithium batteries, compare those figures with the battery-management system rating. For lead-acid banks, check the inverter manufacturer’s recommended battery-bank size and current.

Ask the installer to confirm:

• The inverter’s required battery voltage: 12V, 24V, 48V or another specified range.
• The battery’s operating-voltage range and charging-voltage requirements.
• Whether the battery chemistry is supported by the inverter’s charging settings.
• Whether a communication cable or approved battery protocol is required.
• The battery’s continuous discharge limit and whether it is enough for the intended load.
• How many identical batteries may be connected in series or parallel.

Do not mix different battery chemistries, old and new batteries or incompatible models simply to reach a larger Ah or kWh number. The final connection and protection design should be completed by a competent installer.

5. Check what the quotation actually includes

Some quotes state a battery size without making clear whether it is one module, a complete bank or an upgrade from an existing battery. Ask for a line-by-line description.

The battery price should not be separated from the installation scope. A quote may appear cheaper because it excludes battery protection, cable upgrades, transport, rack or cabinet work, commissioning and the labour needed to integrate the bank.

If you are comparing complete quotations, first read How Do I Check Whether a Solar Quote Is Overpriced or Missing Important Parts in Nigeria? That guide covers the wider quote, while this article focuses on whether the quoted storage itself makes sense.

6. Compare the quoted capacity with the promised backup time

Ask the installer to write down the load used for the backup promise. “This battery will last all night” is not a technical specification.

A useful quote should state something similar to:

• Backed-up circuits or appliances.
• Expected running load or daily energy use.
• Target backup period.
• Whether solar panels will be supplying the load during the period.
• Battery capacity and usable-energy assumption.
• Conditions that reduce the estimate, such as high appliance use, low state of charge or an old battery.

For example, 4kWh of usable AC energy could run a steady 500W load for roughly eight hours, before considering changes in actual load and inverter standby consumption. The same energy could run a steady 1,000W load for roughly four hours. A refrigerator, freezer or pump does not draw its nameplate wattage continuously, so the installer should explain the planning assumption rather than promise an exact number.

If the quote promises long backup but does not show the load and calculation, pause before paying. You need to know whether the installer has sized the battery for your actual use or has copied a standard package.

7. Red flags that the battery capacity may be wrong

• The quote lists only “5kVA system” and does not state the battery energy or battery bank configuration.
• A lithium battery is compared with a lead-acid battery using Ah alone.
• The battery voltage does not match the inverter’s required voltage.
• The quote adds batteries in parallel without explaining current sharing, protection or inverter limits.
• The promised backup time is stated without a load list.
• The installer cannot show a datasheet or exact model number.
• The quoted battery capacity is nominal, but the salesperson describes it as fully usable energy.
• The battery’s continuous discharge rating is lower than the inverter or intended load requires.
• The quote relies on old batteries, mixed battery ages or different brands without a clear compatibility design.
• You are told to remove a fuse, breaker or battery-management protection to make the system work.

A low price is not proof that the quote is bad, and a high price is not proof that it is correct. The important question is whether the equipment, expected service and installation scope are identifiable and technically consistent.

8. Questions to ask before you approve the quote

Send the installer these questions in writing:

1. What exact battery brand and model are included?
2. Is the quoted figure nominal capacity or usable capacity?
3. For lithium, what is the rated kWh, recommended usable kWh and maximum continuous discharge power?
4. For tubular, GEL or AGM, what are the voltage, Ah rating, quantity and bank configuration?
5. What appliances and load did you use to calculate the promised backup time?
6. What battery voltage does the inverter require?
7. Are the battery settings or communication protocol compatible with the inverter?
8. What protection, cables, isolators, rack or cabinet and earthing work are included?
9. What happens if the battery does not provide the stated performance during the warranty period?
10. Will the installer provide commissioning readings, serial numbers, manuals and a handover explanation?

If the answer changes the battery size, price or backup promise, ask for a revised quotation rather than relying on a verbal explanation.

Final checklist

Your quoted battery capacity is more likely to be realistic when you can answer “yes” to all of these:

• I know the exact battery model, chemistry and manufacturer capacity.
• I have checked the right unit: kWh for lithium, or Ah together with voltage for lead-acid.
• The battery bank voltage matches the inverter.
• The estimated usable energy covers my actual critical load and backup time.
• The battery’s continuous discharge capability can handle the load and likely starting demand.
• The quote states the number of batteries and their series/parallel arrangement.
• Protection, cables, installation, testing, warranty and exclusions are written down.
• The installer has explained what may reduce the actual runtime.

If you do not yet know your appliance load, start with the Battery Calculator and then check the result against the exact battery datasheet. If the quote includes panels that must recharge the battery, use the Solar Panel Calculator as a second check. You can also use Can My Solar System Power It? to test whether the proposed system is likely to handle an additional appliance.

The safest decision is not to choose the quote with the biggest number or the lowest total. Choose the quote whose battery capacity, backup promise, inverter compatibility and installation scope can be explained and checked line by line.

SolarPriceNG calculator results are planning estimates. Confirm the exact battery, inverter, cabling, protection and installation design with the manufacturer’s documentation and a competent professional before purchase or installation.