Apropos battery cases...

Rather than go with a lead-acid battery (groan! they weigh a ton) I was thinking that, say, 4 or 5 12v 1800mAh camcorder (or similar) batteries in parallel should work fine. Making a case wouldn't be a complete problem, since acrylic sheets and cement are readily available. But then I start wondering about whether, clamped together, they might overheat and possibly even catch fire. Are there any double-Es posting here who can speak to the subject of overheating and also the subject of ganging them in parallel? (I jumped from p4 to here, so I don't know whether we have EEs posting in this thread)