Battery not charging

I need help - I have a 2003 Sierra w/ a 4.8L that's giving me problems. A few months ago I installed fog lights, back-up lights and a kit to keep the low beams on when I switched on the high beams. 4 months later I saw an error message saying "battery not charging." I took it to the dealer and they wouldn't look at it w/ my aftermarket lights so I disconnected them and error message went away. (I thought) Last week I re-wired the lights and hooked them back up to the battery and all was fine for 2 days. Then the "Battery not charging" message came back, along w/ "Check break booster" and "Check oil." I have since disconnected the lights from the battery, but the error messages still flash and my battery is draining. Sorry for being so long winded, but I didn't know how else to explain my problem. Any help/ideas would be greatly appreciated.

Computor may have bit the dust, the truck is still under warranty ditch the lights and take it back to the dealer, the aftermarket lights may have started the trouble in the first place.