My battery's problem is lateral movement, quite a lot of it. It rattles! The battery lock should be on a cam system to take up wear, rather as camera tripods use.
As a straight lock as Kalkhoff use is not up to the hammering that their bikes get on English roads. The problem with the method suggested here is that it involves pulling off and re-fitting rather brittle bits of seemingly cheap plastic covering - like car trim they seem tailored to factory fitting and cosmetic needs rather than maintenance.
My method is not pretty but it does work reliably and will do so no matter how much wear on the lock interface.