I am not electrically savvy - is a 100 amp alternator needed for those H-4 bulbs (60W, 12v, 5amp draw each)?
Or, is the 100 amp needed for other 12v volt devices/accessories?
On a simple swap to halogen lights, I do not think an alternator upgrade would be needed. But if your total amp draw load for lights and a bunch of other stuff exceeded the capacity of the original alternator, then the battery would slowly draw down. Think of it as filling and emptying a bucket at the same time. If the emptying flowrate exceeds the filling flowrate, then the bucket will eventually be empty.
I doubt that a lightly modded stovebolt electrical system would need a 100 amp alternator, but if someone stuffed a monster amp sound system in the back, that would be another story, and maybe the alternator would need to be upgraded (or turn off the tunes to allow the alternator to recharge the battery, then turn them back on.)
