Luckily I found out with WATCH sized batteries...
I made a blinky bug (THe Cool Useless Product out of this/last months Popular Science) and I was soldering the antennae onto the battery.
The first one got to hot and exploded (Luckily it wasn't a big explosion, it just sorta popped with a small alkali flame burst. (The two halves split nicely, and no harm came of me, thanks for asking!
The second battery I was more careful with, and I didn't let it get too hot.
But the Brand new Li-Ion had no more voltage or current. The heat of the Iron completely killed it.
For my portable I'm considering Li-Ion batteries, but if I solder them will they mess up too? (It's not so much a COMPLETE battery loss I'm worried about as a small/moderate loss in mAh or voltage)

