Based on my experience with these basses (I have owned 4 of them over the years) I have to agree that if you leave a cable plugged into the bass, the battery is "on" and it will lose it's charge. Best practice is to unplug it when not in use.
Well, that's good enough evidence for me!
BTW. if you don't mind me asking - why did you buy and then get rid of this model so often? Was there something you didn't like about it?
Also, just got notice of an eBay sale for it 1980 Yamaha BB1200S electric bass vintage Japan active | eBay if you're into a reacquisition...
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