Undervoltage turn off consumers
 

2003 c240 66,000miles
when i cut on the auto ac button while running the stereo in the 108f heat here i get the undervoltage turn off consumers light, if i turn it back to regular ac, ie turn the auto button off the light goes off. i don't have any dimming of lights or any devices not working. my question is will this problem correct itself if i don'r place too many electrical demands on the car at once. and if i drive it around enough for the alternator to fully charge the battery?the dealership i bought from said the battery and alternator were tested out before i bought it, when they did the whatever-point inspection before putting it on the lot. i've read here that it could be the voltage regulator, the battery or the alternator. i don't trust pepboys to replace battery as they could blowsams module. also i don't have the owners manual with radio codes, etc. also, i should add that this car was at a dealership for about three months with people test driving it for only short trips. doesent this car loose something like 1% of its battery per day if its sitting,to keep all the gizmos running?what is it usually with this year and model when this problem arises. i am a non-mechanically inclined person, advice please
thanks
j