I have a stock 07 5.9 that has never given any electrical problem. I recently started pulling a 5th wheel camper that has 2 batteries in it. About 50 mi down the road, the check eng light came on the code was P0541 (heater relay under voltage). I cleared the code and it came back next time I hooked the 5er up to it. My previous 5er only had one battery and I never experienced the code. I suspect the alternator cannot handle that many batteries. Any thoughts on that and is there a higher capacity alternator out there or can you add a second alternator. Thanks for any help or input.
Ron