0.8mA is perfectly acceptable for background current drain. This would not cause your battery to drop in voltage from 12.79 to 12.4V over 25 days.
The odd thing in your case is that the voltage drop is the same with all the accessories disconnected. USB sockets are a notorious problem for draining batteries if not isolated or ignition-switched as the step-down transformer in them can consume up to 50mA even with nothing plugged in. It can't be this though as the voltage drop is the same when disconnected.
Quote:
Originally Posted by
Mathias
The battery is not original, it's a Bosch M6 011 (12V, 8Ah, TTZ10S-4 / TTZ10S-BS), but it should be 6 months old and what I know completely drained once when I received the bike (could not be started then, just some relay clicking).
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It could be explained by a failing battery though if it has suffered internal damage/sulfation to the plates, diluted/contaminated electrolyte or has a higher internal resistance than it should from being completely discharged for a period of time. The internal resistance forms a voltage divider with the load. It is only when a load is applied that internal resistance comes into play. When disconnected from the bike there is no current drain at all, so everything is fine and no, or very little voltage drop is noticed (and will test as such on a battery tester). However, as soon as it is exposed to a current drain, however tiny, the internal resistance influences battery voltage negatively. If a battery is past it's best this resistance will be higher than normal and cause the voltage to drop more rapidly, which is I think what you are seeing.
It's actually a lot more complex than this. If you're interested in the equations and the science behind it then have a read of the attached PDF.