I had the Oxford Heaterz Premiums on my '75 R90/6. Never had a battery problem, but I watched it closely and put the bike on a trickle charger weekly or so to keep it topped up. Enjoyed the grips very much and they lengthened my riding and commuting season significantly.
When I bought my V7 Stone last year, I bought the wrap on version of the Oxford grips. They can be installed and uninstalled in a few minutes and provide plenty of heat to the palms of my hands. There is no heat level control, just on and off, so I use that to regulate the heat for comfort.
Both types of gri.ps have one big drawback: they do not warm the back of your hands, which is the part that faces the wind and gets cold quickly when riding at speed, even with well insulated gloves. Heavily insulated gloves will also restrict the amount of heat getting from heated grips through to your palms, but it wil make it through (like heated car seats warm you through your winter coat).
Having cold hands is a major health problem for me, so I need to watch out for them all the time. This winter my wife bought me heated glove liners. The wiring that heats up in the liners is over the back of the hands, which is a big plus, keeping the hands warm while adding hardly any thickness or bulk and enabling easy working with tools, etc. out of doors. Since they are glove liners, you can wear any glove or mitten over them, depending on what you like or need. This keeps the expensive liners from excessive wear, too.
The ones she bought use 12 volt batteries, so can easily be bike powered. I have been using these gloves all winter and really, really like them. My hands are warm and the liners are thin enough that I can work outdoors with equipment, or just moving snow or walking the dog, with ease, safety, and warm hands. I just got cables to wire in the gloves to the bike. As soon as the ice and snow retreat here, I'll be trying out the glove liners along and with the Oxford grip wraps on the bike.
The glove liners were developed for bicyclists, but are used in industry and by lots of others. They can be found at:
http://powerinmotion.ca/Products/HeatedWear/Heated_Gloves_Calgary_Toronto_Vancouver_CanadaI have no connection with the company. I'm just a very happy, warm-handed user.
Stephen