In short
- State of health compares today’s usable capacity with the capacity when new; it is an estimate made by the BMS.
- It moves slowly and not always smoothly; a single reading means little, the trend over months says a lot.
- A record of health, cycles and temperatures documents how the battery was used.
WeCo backs its batteries with a long warranty, often expressed in years and in energy throughput or cycles. Over that time the cells lose a little capacity, as every lithium cell does. The state of health, or SOH, is how the battery management system expresses that loss.
What the number means
A state of health of 100% means the module still holds its original capacity. At 90%, it holds about nine tenths of it. The BMS cannot weigh the capacity directly; it estimates it from what it observes during charges and discharges. That is why the number can stay flat for months, then step down by a point, and occasionally even step back up after a full charge corrects the estimate.
How fast it should move
Capacity fade depends above all on three things:
- Temperature. A battery kept cool ages more slowly than one in a hot garage.
- Time spent full. Long hours at 100%, especially warm, cost more than the same hours in the middle of the range.
- Energy moved. Each cycle wears the cells a little. Deep daily cycles count more than shallow ones.
A healthy home battery loses capacity gradually, a few percent over the first years. A sudden drop, or one module falling much faster than the others, is worth a question to your installer.
Reading the trend
| What the record shows | What to make of it |
|---|---|
| All modules moving together, slowly | Normal ageing |
| One module dropping faster | A weaker module, or one that works warmer |
| A step down after a hot summer | Heat has a cost; check where the battery sits |
| Health rising again after a full charge | The estimate has been corrected, nothing more |
Why a record helps
If you ever need to make a warranty claim, the conversation is easier with data: the health of each module over time, the number of cycles, the temperatures it lived in. Without a record, it is your memory against a datasheet.
WeCo Monitor reads the state of health, the cycles and the temperatures of each module, and the free Cloud keeps up to three years of it, exportable as CSV. Home Assistant can send you a short summary once a month, so that slow changes do not go unnoticed. The box only reads; it never changes anything in the battery.
Common questions
My battery shows 100% health after two years. Is that right?
It can be. Some systems keep 100% until the estimate has enough data to lower it. Watch the trend over the following months.
Can I improve the state of health?
Not really, but you can slow the loss: keep the battery cool and avoid leaving it full and warm for long periods.
Is the Cloud history mine?
Yes. You can export it as CSV at any time, and stored readings are deleted on request.
