Blog - LiFePO4

Comes winter, most of you are interested in what is the battery capacity in lower temperatures, what is a discharge and how to charge your battery. We will try to sum it up for you and will start with battery capacity.

Battery capacity

If the temperature in the place where your battery is stored reaches somewhere from 10°C to 40°C, the battery nominal capacity is 100%. For temperatures below 10°C the internal resistance of the battery increases and as a result the total capacity decrease. For example at 0°C, the estimated available capacity is 90%, at -20°C, the estimated available capacity is 70%.

Low voltage disconnect (Underload)

If it comes to the discharge voltage levels they change according to the temperature where cells are stored too. At 0°C the low voltage level changes from 2.8V to 2.4 and for example at -20°C, it drops from 2.8V to 2.0V.

Charge and discharge

It is possible to discharge a battery at any temperature, but it is necessary to be aware that with a bigger load at low temperature, the battery voltage may drop by one volt. It is necessary to set BMS for this drop voltage. We recommend doing a standard charging at least at +5°C. The temperature under +5°C causes increases battery internal resistance and it is necessary to charge it with maximal current 0,1C. At 0°C temperature and below, we don't recommend charging the battery at all.

Overall, should you have to use your battery in a cold climate, we have some tips on how to operate your system in order to avoid any damage or malfunction of your batteries. 

You should make proper thermal insulation of the pack so that the pack does not lose temperature in a cold environment and you also should arrange for the pack heating (during charge). The properly insulated pack may be preheated to a quite high temperature (even to 30*C) to absorb the thermal energy. This way the properly insulated pack of large capacity may stay warm for several days and may use some part of its energy to warm itself before or at the beginning of the operation in a cold climate. It is usually around 5% to 8% of the energy that may be used to increase the temperature of the properly insulated battery pack.

On the chart below you can see the behavior of Winston battery voltage and capacity drop during discharge at different temperatures.