I am trying to set up a logic system that shuts off my generator when the battery is full and turns it on again when the battery is empty and I am noticing a problem -- the battery can hold 4000 J, but despite me producing more than I'm consuming (the battery will fill up when the generator is running, despite some devices being on and draining) the battery actually never reaches 4000 J, so the "full power" logic output never comes on and so my "turn off again until empty" latch never triggers.

When I repeatedly inspect the battery, it seems to be floating at around 3937.3 J - 3949.5 J:
https://steamcommunity.com/sharedfiles/filedetails/?id=2871890968

Is there a solution to this, like being able to read the power stored and make logic for "when stored > 3900 J" or something like that?

It works when there are no devices consuming power, as the battery is then able to make it to exactly 4000 J, but that's not really a desirable special case.