[thstone]

Ok, got out my handy Bosch Fuel Injection and Engine Management book (everyone has of these, right?) and the ECU will also slightly alter the ignition timing based on battery voltage. The logic is that lower battery voltage will not charge the coil packs as quickly. The goal is to maintain constant current in the coil packs so as not to overheat them.

With all of this being said, P1126 is oxygen sensing adaptation range 1 (cyls. 4-6) at enrichment limit. I doubt that this code is the result of a bad battery alone, so its probably two separate problems. But go the easy route and replace the battery and see if that fixes the problem. These integrated engine management systems can create somewhat strange symptoms based on simple problems. If not, then proceed to look for a vacuum leak, bad MAF, etc.