Spoiledbiker.com sells an adapter thing (looks a little homemade, but I'm sure it works) that allows you to hardwire a Kenwood FRS radio to a 12v line. I actually contacted several branches of Kenwood and Motorola's customer service people to inquire about radios that had dedicated 12v power connections, and neither manufacturer offers anything like that. They all recommend "just use our nifty rechargeable batteries and carry the charging cradle, power adapter, etc. with you"... Yeah, right!
This is what I bought: http://www.amazon.com/MIDLAND-75-822...9521289&sr=8-2
It's about $63 bucks, comes with three power source options (AA batteries, rechargeable Ni-Cad pack, and a cigarette lighter plug) and works with it's own rubber antenna or an external antenna.
I use mine mounted on the side of my topcase with the rubber antenna in place, and it works great. It's wired into my StarCom (they make a dedicated cable for it, just like AutoCom and others) and is actuated by my handlebar-mounted PTT button.
The only downside to this mounting option is that I cannot make changes to the channel, squelch or volume while moving, but that has not proven to be a big problem. I'm considering moving the radio unit to the front of the bike at some point, and using the antenna adapter to run a FireStick antenna mounted on my rear subframe. That will tremendously boost the range of the radio and allow me to operate the radio controls on the move.