maintaining 12v battery

An over night charge at 2 amps would be fine anything between 8 and 12 hrs in the middle of that ten day period or seven days of none use would be ideal. If your car is parked outside consider a small solar charger permanently attached and placed under the rear hatch window. This would save you having to think about connecting the charger.

 

Britprius made a very good suggestion.

Also how old is the accessory 12v battery? It might be on its last leg & due for replacement.

 

The Optima is safe up to 10 amp charge so 2 amps will do it no harm at all. The OEM battery can only be charged at a maximum of 4 amps "the reason I suggested 2 amps" but a nice slow charge on an AGM battery is always better than a fast charge.

A small solar charger could still be used if the panel could be put outside the garage doors and the wire run to the front or rear of the car "perhaps with a none reversible plug and socket permanently wired". A 3 watt 12 volt panel would supply 1/4 amp during daylight hours, perfect for keeping it topped up.