I'm ready to add one to my '01. Need suggestions on where to buy a decent weatherproof, simple and not too expensive unit.
Matters if you want digital or analog. I personaly prefer digital, as I like knowing if I'm at 12.4 or 12.6 volts. No guessing there. I used this one:
I had it connected to the accessory leads in the headlight bucket, and it was on all the time. (the unit uses so little power it would take months to lose enough charge that you couldn't start the bike)
This was very handy IMHO , as I could see how much charge was on the bike before I even started it, confirm the battery was getting a charge while on the battery tender , and I could moniter the slight variations when running with my driving lights on or the load on the system in heavy traffic.
I of course mounted the gauge to my dash, but you can easily mount it to a small plate and fit it in around the instruments.
There is also the popular Datel meter, that has backlit LED's, you would likely want to run this off a relay unless you ride every day or so:
These are mostly mounted on bikes with fairings, but you could use a small plastic project box from radio shack or something simular.
I think all bikes should come equiped with voltmeters, but you don't have to have one....but it is highly reccomended if you plan on running any electrical devices off your bike like extra lights or heated gear.