Battery Voltage, Capacity & Sizing

How to read a battery label, work out runtime, and choose the voltage and amp-hours your application actually needs.

Start with the arithmetic

battery voltage guide →
battery capacity runtime →
battery sizing by application →
battery group sizes bci →

Voltage & sizing questions

The questions that come before an order.

What voltage should I choose for a lithium battery?

It is set by the equipment: 12V for small loads and vehicles, 24V for light traction and vans, 48V (51.2V) for storage and most traction, higher for industrial systems. Match the device first, then choose amp-hours.

How do I work out runtime from amp-hours?

Multiply amp-hours by the nominal voltage for watt-hours, then divide by the actual load in watts. A 48V 100Ah pack is about 4.8kWh, which at 500W is roughly nine hours.

Is a higher voltage always better?

No. Higher voltage means lower current and thinner cable, but it also changes the charger, the BMS and often the whole system. Step up only when the equipment or the cable run demands it.

What does C-rate mean?

The current expressed relative to capacity: 1C on a 100Ah battery is 100A. Discharging faster than the cell rating shortens life and usually trips the BMS.

Why is a 12V lithium battery labelled 12.8V?

Because LiFePO4 cells are 3.2V nominal, so four in series give 12.8V. Equipment designed for 12V lead-acid accepts that range without modification.