What do you expect squirting it with a hose will do???????

Well if there is actually Lithium metal in the battery water should make for a nice fireworks show.

I don't understand You had 7.8v .........Thats was a good lipo 2cell battery to me.
Anything from 6v to 8.4v is good and should work ???????

I punctured one (acidentally) and it went off (oxidized at high rate) - unbelieveable amount of white cottonball smoke and it got very warm. This was about 3 yrs ago and was 2 generations older than what's on market now. Be careful, you might not get much chance to hose it after you cut it open if they still react to oxygen exposure that way.

Lipos have to have less than 3grams of lithium in them, other wise they'd be considered hazardous good and cost a premium to ship and you'd not be allowed to fly them at all. What I've read, the lithium is much less than that in an individual lipo and is decreasing from generation to generation. They are getting safer because of it.

You might be more entertained by hooking it up to a power supply and hitting it with 20-25amps......