The onboard voltage meter was reading 12.1 volts before I started to configure my gps, the engine is not running so the gps is running off one of the batteries, either the one I have attached to the external plug or the onboard battery. After 15 or 20 minutes the voltage meter onboard is reading 11.6-11.7. I assumed the plane was using the external battery, but the next time I use the airplane with no external battery connected the voltage meter read 11.7, so assume it was actually using the airplanes battery. I have a avionics master and a master and the master master has to be on to power the avionics master. That fires up everything, and the power draw is a little heavy, the only thing I can turn off is the second radio with pulling circuit breakers. I understand the updates for the avidyne hfs can take this long, I would not to use the onboard battery.
I do have have a battery minder charger and a one year old canacord battery.