# How to detect LiFePO14 12V battery capacity and charge/discharge current?

I have no-name 12V LiFePO4 battery from Aliexpress and I don't know it capacity and charge/discharge current (I don't believe in params that Chinese seller wrote). How can I detect it?

Safe charge/discharge current can only be guessed. The best way to guess is to use capacity and limit to some safe value, like 0.5C. 0.5C means two-hour discharge, i.e. if you have 50Ah capacity, discharge current would be 25 amperes.

If you don't know capacity, you must measure. You need an electronic load that applies a fixed current and measures the time until the voltage runs down to some setpoint.

Charge the battery to full charge first, limiting max charging current to very small value so you don't charge it overly fast. Best guess for charging current would be to measure the weight of your battery, look at LiFePO4 battery specs of similar weight and voltage and use their max charging current, then perhaps divide by 2 or 4 for safety. You can also look at specs of max charging voltage of other LiFePO4 batteries and use that value, or simply by using a LiFePO4 charger.

Then apply the electronic load. Look at sources for minimum safe LiFePO4 voltage and set that to your electronic load. Set the current to some safe value, by measuring the weight of your battery and looking at specs of different LiFePO4 batteries of similar weight and voltage and using their max discharge current.

The electronic load will tell you the ampere-hour capacity of your battery.

Cheapest electronic load components for prototyping use could be bought for as little as ~30 USD, but good electronic loads easily cost 500-1000 USD. For example, where I live Siglent SDL1020X-E can be bought for about 550 USD.

If you are unwilling to spend on an electronic load, the only way to measure capacity is to weigh your battery and look for other LiFePO4 batteries of similar weight. That's a guess but could be enough for you. At least much cheaper than electronic loads.