This is going to sound like a wise ass answer but it's not. After you run down your battery a few times, remembering to unplug it should become easier.
There are a lot of active bass detractors who point out the risk of a battery dying in mid gig and the kind of tragedy than can result as primary reasons for playing passive basses exclusively. It's my opnion that that's a FAR less common occurrence and a much less sever problem than the detractors make it out to be. If you play an active bass, part of being prepared at a gig is having a spare battery in your gig bag. When/if you detect unexpected distortion or a fading signal, you simply change batteries at your earliest opportunity (after that song, or after the set) and you're good for another year or so. I've never detected it, but I'm prepared.
Against, just to reiterate, my first paragraph is NOT intended to be a wise ass answer. If unplugging your active bass after playing it isn't a habit in the beginning, running down a battery or two WILL help it to become a habit.