For the past few weeks, our battery has been charging up to 100 per cent during the day and consumption from the grid has been a few pence a day. Suddenly last night we used £2 worth of mains electricity and when I look at the graph I see that at 0200 the battery percentage fell off a cliff. 
](https://) Can anyone please suggest a reason for this?
What BMS version are you on? If 3007 you could be seeing the SoC drop here: https://community.givenergy.cloud/d/713-firmware-3007-has-not-fixed-sudden-soc-drop-to-0-problem/2711
It seems to be 3008. I noticed when looking for that information, that updating the battery firmware would cause it to discharge completely - which is what this looks like. I can't see any setting to allow me to control this, for example to stop it happening in the night and force it to do so during the day while we are generating!
The battery calibrates when the FW is updated. Full discharge to zero followed by full charge to 100%.
I saw this also last night on our system - battery dropped from 20% straight to 0% at around 5am.
We are on battery firmware version 3008
Givenergy please advise
Petergroves81 A full battery discharge would take time i.e. it would export the energy to the grid over an hour or two.
The graph you've shown looks like a bug of some sort - very similar to my graph btw.
Ita the SoC drop...there's a massive thread on it here and GEs months and months of excuses and eventual (partial) fix.
I have a similar observation but it drops to zero then straight back up, is this related?
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Ah ok great thanks