Battery not holding charge despite replacing alternator, and both new super duty batteries. Mechanic cannot find sourse of battery drain.
There is not much we can do from here. The only thing that comes to mind is that something may be sleeping most of the time and is not detected because it is not using power when someone was looking.
I might add that not all mechanics are as good as others at finding these kind of problems. You may need a different mechanic.
Are both batteries hooked up all the time or is there some kind of switch?
Both batteries are always hooked up. One of the mechanics told her she needs to drive it more often. It sits at a horse training facility, in front of the horse trailer. Since it’s a diesel, could he be correct? However, after using it myself to haul a horse over 75 miles and back, the very next day the truck would not start. And it wasn’t cold weather here.
Has your mechanic checked to see how much current is flowing from the batteries with the engine and everything off? Is it possible a glove compartment light or something similar is staying on? If the truck is still drawing significant current with everything off, all doors shut, etc. (probably more than 100mA would be bad), then the next step is to start pulling fuses until the current drain disappears. Then you’ll know what circuit is likely causing the problem.
Great tip. I just sent her your latest post and suggested she get in touch with her mechanic and also find a new one perhaps. This has been going on for almost a year!!! Thank you so much.
Usually more than 30 milliamps of current drain after things have gone into the sleep mode is a sign of trouble. Here is a link that is helpful with this kind of trouble.