In short
- LiFePO4 cells age faster when they live hot; the room matters as much as the battery.
- Watch the battery’s own temperature over a whole summer day, not just at noon.
- Shade, airflow and distance from the inverter usually gain more degrees than any setting.
A battery does not fail because of one hot afternoon. It ages a little faster for every hour spent hot, and the effect adds up over years. That is why two identical batteries can show quite different health after five summers, depending on where they stand.
Where the heat comes from
Three sources usually add up: the room itself, a roof or a wall in full sun, and the inverter next door, which gives off heat while it works. A battery placed right beside the inverter in a small metal cabinet can sit 10 °C above the room temperature on a busy afternoon.
What to watch
Felicity Monitor reads the temperatures the BMS reports and keeps them minute by minute. Look at a full hot day: when the battery is warmest, and how far above the room it climbs while charging at midday. A battery that stays within a few degrees of the room is well placed. One that climbs well above 40 °C every afternoon is telling you something about its corner.
Simple fixes that help
- Keep the battery out of direct sun, and away from walls that take the afternoon sun.
- Leave space around it and between it and the inverter, so air can move.
- In a closed cabinet, a small fan on a thermostat or a smart plug often lowers the peak by several degrees.
An alert for the hot season
Set a notification when the battery passes 45 °C for more than fifteen minutes. If it arrives often, the battery needs a better place, not a better setting. The free Cloud keeps the history, so you can compare this summer with the last one after you have moved it.
Common questions
What temperature is too hot?
Check Felicity’s specification for your model. As a rule, the closer the battery lives to room temperature, the longer it lasts.
Does the box measure the room temperature?
No. It shows the temperatures the battery’s BMS reports. A room sensor in Home Assistant is a useful addition.
Can Home Assistant switch a fan when the battery is hot?
Yes, with the battery temperature sensor and a fan on a smart plug.
