Battery %age drop

We've noticed our battery drops off quite markedly, without there being any noticeable drain on from the system. This has happened a number of the times over the past month or so. In the graph below, from the early hours of this morning, you can see the battery percentage dropped from 28% to 12% in a little over half an hour. There's no power spike showing in the graph, just the regular overnight usage of 500-600W.

Is it indicative of a faulty battery? We have a 13.58 kWh (4 Battery Packs) All-In-One Inverter/Battery unit. Could one of the battery packs be failing?

[unknown] Is it indicative of a faulty battery? We have a 13.58 kWh (4 Battery Packs) All-In-One Inverter/Battery unit. Could one of the battery packs be failing?

Not necessarily - it is a common problem that the BMS is not very good at tracking the true SoC - the estimate is based on tracking energy in/out, and it is only when the battery visits the extremes of full and empty that it can reorient itself. But when it is idle, it also gets a chance for introspection, which can result in adjustment of the estimate.

Advice seems to be to try to exercise the full capacity of the battery from tine to time.

Pretty normal. Basically at that 28% point the system detects that there is less stored in the battery than the SOC value it has been showing, as things adjust you get a more rapid reduction in SOC despite the load not changing.
If there is a sustained period with good solar I find my system doesn’t drop below 50% capacity - after a couple of weeks I find that when it does next drop below 50% ‘m likely to see one of these adjustments.

Through winter months my battery generally hits 100% and 4% daily and keeps better check on the SOC.

Thanks for the input guys. Glad to hear it's most likely not a defective battery <phew>.