[Commuta_Busa]

to answer your second question, it doesn't matter where you ground it as long as it's a good solid ground.

as for the voltage loss I would have to guess it's one of two things... your alarm is sucking down the battery or your battery is slowly loosing its charge. I would say it's more likely to be the alarm though. Batteries these days last pretty damn long esp sealed ones. Check what the amperage draw is while the bike is off this should be a good starting point.