I think it was the ZX81 (and later the Spectrum) where my brother and I had it hooked up to the mains on my parent's boat. The problem was there was only one 12

I think it was the ZX81 (and later the Spectrum) where my brother and I had it hooked up to the mains on my parent's boat. The problem was there was only one 12V battery (via a voltage regulator) which not only powered lights and our computer, but also served the engine. If we were sailing and the wind dropped, we established a protocol where my Dad would have to give sufficient notice for us to save whatever we were working on to tape before he started the engine, as the starter motor drew enough current to dip the voltage below the 9V the ZX81 needed, thus causing it to crash. And of course, RAM wobble wasn't helped if there were heavy waves. It's amazing what we put up with just to get some computing time.