Couldn't Scotty mod up an aquarium out of transparent aluminum for you? He'd also solve the electicity & water problem.
Forget the battery, remove it. Install a "water4gas" kit on your Prius and feed it from your aquarium. It'll never run out of water for 20 years!
What makes me mad? The use of the phraseology..."such as an aquarium"...that means it's not limited to just an aquarium. You can't put a hot tub back there, or a cistern with water for the Orphans... If the orphans get thirsty...I'm blamin Prius....
Ask Davis "Fishman" Rivera who built a career on incorporating aquariums into high-end stereo installations after winning his class in the 1991 IASCA Finals. Backseat (seat backs laying down) of a 1989 Toyota Corolla