Depending on configuration, e fans are liable to pull 50 or even more amps on high speed. Your stock alternator is rated to charge at 105 amps, and considerably less than that at idle and into the cruising RPM range. You can see how this would cause a problem. The big 3 would be a start, but you really need a bigger alternator and ideally a good battery (or two if you really want to upgrade.) I run Deka AGM batteries in every vehicle I own. Roughly the same price as the Napa legend I swore by for so long, and they perform much better. The legend used to be a great battery, these days much less so.