What kind of length rides are you typically going to be using it on? That could make a big difference on whether a battery powered one will work for you or not bceause the battery will only last so long. I bought the Gerbing's battery powered microwire vest about this time two years ago, along with an extra battery. I mainly use it commuting on the bike (about an hour each way on the interstate) and it suits me just fine. It's got two heating panels on the chest, and one in the middle of the upper back. So coverage isn't as much as you'd get with one that hooked into the bike's electric system, but it's a tradeoff to keep battery life acceptable.
Battery life greatly depends on what setting it's on. 50% seems to be good for a real gentle heat; enough that I notice it's there if I think about it but nothing too crazy. I figure I'll probably get around 4-5ish hours out of the battery at that setting, though I've not left it on long enough that the battery died.
Once the temperature outside gets much below 40F, I usually set it at 75%, and the heat is much more noticeable. It lasts probably in the 2 1/2 to 3 hour range or so at that setting.
I almost never have it set up at 100% as it gets pretty toasty at that setting and kills the battery pretty quickly; probably no more than 1-2 hours at that point.
Overall I rather like it and it works well for my typical use, though I'm considering a full plug-in jacket liner as I think I'd like to have heat on my arms as well.