I have connected 2 of these in series for a 24 volt system. I checked the voltage on both before installation and they were the same. After running for about 8 weeks the one battery sits at 13.9 volts and the other at 13.2 volts. I have been looking for a battery equalizer/balancer but can't seem to find anything. I am now buying a charger to charge both batteries to max and will then reconnect them. I do however believe they will become unbalanced again. Any advice please?