I don't get on with active basses — I much prefer passive, but when I used to regularly play an active one I came up with an idea to get around this issue. I never built it, but the design would have been a short length of cable with an inline switch in the middle, a stereo jack plug at one end, and a mono jack socket at the other. The cable from the amp goes into the socket, then when plugging the jack plug into an active bass with the switch set to off the battery in the bass stays off until the switch is set to on. I never bothered to build it as it was easier to just unplug the blummin' bass when it wasn't in use. While typing this up, it just struck me that this could probably be better built as a pedal with a footswitch where the amp connects via a mono cable and the bass via a stereo cable.