I can say from experience with wheelchairs, the second battery that connects to the controller is usually the lower one of the 2 for 24 volt operation.
When they are out of balance, I discover my battey meter moves more when under a load or not, then when they are equal. To equal them, I have a small charger I hook to them in parallel for about 6hours or the meter reads low to fully charged then it started. I find I have to do that weekly. Maybe I am not getting 2 equal manfactured batteries in the process with I buy them? Ive heard from other wheelchair users that the second battery is usually lower then the first one. Ive, myself seen from a full volt to 2 decimal places of difference. jeff richmond, va http://www.wheelchairmodifications.org
