Solar Batteries Explained: kWh, Voltage, Amp-Hours and Depth of Discharge
Battery listings are full of numbers: 48 V, 200 Ah, 10 kWh, 80% DoD. They are not hard to understand once you know how they connect. This guide covers the terms that matter when you are comparing solar batteries.
Energy versus power
- Energy (kWh) is how much electricity the battery can store, like the size of a fuel tank.
- Power (kW) is how fast the battery can deliver it, like the flow from the tap.
A battery can have plenty of energy but limited power, which means it cannot run several big loads at once. Check both numbers.
Converting volts and amp-hours to kWh
Many batteries are listed in volts (V) and amp-hours (Ah). To get energy:
kWh = volts × amp-hours ÷ 1,000
| Battery | Calculation | Energy |
|---|---|---|
| 12 V, 100 Ah | 12 × 100 ÷ 1,000 | 1.2 kWh |
| 48 V, 200 Ah | 48 × 200 ÷ 1,000 | 9.6 kWh |
| 51.2 V, 200 Ah | 51.2 × 200 ÷ 1,000 | 10.24 kWh |
The Sunpal wall-mount battery in our catalogue is listed as 48V/51.2V, 200Ah, with a 5–15 kWh range in the title. The arithmetic above shows how those numbers relate. Confirm the exact capacity of the variant you are buying on the datasheet.
Nominal versus usable capacity
The label capacity is usually the nominal capacity. The part you can actually use depends on the depth of discharge (DoD) the manufacturer recommends.
As an illustration only, a 10 kWh battery with a recommended 80% depth of discharge would offer 8 kWh of usable energy. Different batteries and chemistries have different recommendations, so use the figure in the manufacturer's documentation and do not assume.
System voltage: 12, 24 or 48 V
Your battery voltage must match your inverter or charge controller. Higher system voltages carry the same power at lower current, which allows thinner wire, lower losses and less heat. That is why larger systems typically use 48 V. Small RV and camping systems often use 12 V.
Other specs worth comparing
- Continuous and peak discharge power: the loads it can run at once.
- Maximum charge current: how quickly it can accept energy from your panels or inverter.
- Round-trip efficiency: some energy is lost going in and out of storage.
- Cycle life and warranty terms: how many charge-discharge cycles the manufacturer states and what capacity it expects to remain at the end of that period. Read what the warranty actually covers.
- Operating temperature ranges: particularly the charging range. See our guide to lithium batteries in Canadian cold.
- Communication and compatibility: whether the battery works with your inverter's communication protocol.
- Certification: Canadian marks for the exact model.
Putting it together
Suppose your daily use is 4 kWh, you want one day of storage and the battery you are considering has 8 kWh usable. That covers about two days on paper, before losses and winter margin. Treat this as a simple example, not a sizing rule. Our energy-use guide explains how to find your daily figure.
Common mistakes
- Comparing batteries by price per kWh nominal rather than usable.
- Ignoring discharge power limits.
- Buying a battery voltage that does not match the inverter.
- Forgetting the cold-weather charging limits.
To see what is on offer, browse the batteries and energy storage collection, or the Sunpal hybrid home solar system with a 5kWh lithium battery, which is listed as a complete set. Request the datasheets for the exact items you are considering.
This article is general education, not electrical advice. Always rely on the manufacturer's datasheet for specifications and operating limits.