On my tin rig, i've got 2 identical group 27 wet cells wired in series to run a maxxum 24v trolling motor. The big motor is cranked off the low side battery in that pair. I fished till past noon Saturday, on the trimming motor most of the day, and in current at times. Sunday we anchored up by a brush top and let a kid drowned crickets. Only bumped the trolling motor on low a few times thru these morning. When I got home, I decided to charge the batts with my portable charger instead of the on board charger (because it is only a 4 amp per bank noco). Keep in mind, this was hours after I was done fishing. To my surprise both batteries showed fully charged. I can see how the alternator could charge the one batt in the group that it's connected too, but the other should be down significantly. I got the volt meter out and that confirmed the one that is used as a cranking battery as well was at 13.0V and the other at12.9V. Those numbers sound high?