When I sit in traffic with the brake lights on and the radio pretty crankin', the truck will idle very rough until I bring up the rpm's. (takes about 1-2 minutes for this to happen)

This is the 5th time it has happened and I finally realized today that this is the cause.

Does this indicate a weak battery or am I just pushing the alternator too hard? Maybe a large cap will help? The headlights flicker a bit but nothing crazy.

Anyone else experience this? The amp is 800 watts + the radio draw. I have had this setup for over a year.

Lew