What kind of batteries do I need for solar power?

What should I buy??

When you are building a solar power system with a battery bank, an essential question is what kind of batteries should you buy. This post will explore.

Fortunately, this seems to be a really straightforward decision. In pretty much every category you likely care about Lithium Iron Phosphate (LIFePO4) wins handily over Lead Acid batteries. They are lighter, cheaper, have more capacity, and longer warranties. 

The one factor you want to pay attention to for LIFePO4 batteries is their vulnerability to cold. Charging LIFePO4 batteries below  0°C/ 32°F can damage them, unless this vulnerability is mitigated.

LIFePO4 batteries can be protected from cold in various ways. Ideally combine both for peace of mind:

An insulated enclosure, with a small heater

It is increasingly common for LIFePO4 batteries to offer a built-in heater. This feature means when the battery drops below 0°C/ 32°F, the heater turns on. If your battery bank does not include this feature, you can build it in with an insulated battery enclosure and small heater.

Many people fund that within an insulated enclosure, the heat given off by their equipment is sufficient to prevent the batteries from dropping below 0°C/ 32°F.

Low temperature cut-off 

Many battery management systems (BMS) have a low temperature charging cut-off built into them. Even if your battery’s BMS does not, a lot of charge controllers and charger-inverters have this feature as well.

The following table lays out the comparison between battery types for each attribute:

To wrap up, LIFePO4 batteries make a lot of sense. We’ll do a future blog post if the situation changes, say from the arrival of even better new technology.