Death fumes?
Well, no.
Explosive?
Yes. But only in a confined area. Keep in mind, it's not going to fill the cabin with explosive gas. But if you have a spark close to it, there is a possiblity of explosion. This is usually a problem with a battery being recharged from a very discharged state.
Truthfully? Your stock system is probably adequate for what you want. Just add a voltmeter so you can watch the battery and stop using it before it drops too low.
Look into an optima battery too. Good stuff there...............
Optima Batteries