[adept-I]

I'd suggest recharging the battery/checking to make sure that the "cells" in the battery are all topped up (to a level just to the bottom of the filler necks) as often storage of a vehicle for a period of time, particularly in warm climates, can lead to evaporation of the charge retention fluid (a mixture of electrolytic acid and distilled water) that you can see when you pop off the caps on top of the battery.

Give this a shot and if you've still some concern about the altenator, most auto parts stores offer free in-car testing of the altenator..., good luck.