I cant believe I can't remember this but when you connect batteries in series, do the amp ratings add up or does it stay the same and the voltage just go up?
Eg.
If you have three 12 volt 10 amp/h batteries in series, do you get 36v 10 amp/hr or 36v / 30 amp/hour?
Think about it. When the batteries are in series, each has the same current. So the total amount of amps (amp-hour not amp/hr) would be the same, so the AH rating is the same as one battery but the voltage doubles, of course.
In series, the voltages add up. The current capacity is the same as the lowest of the batteries.
In parallel the current capacities add up. If the voltages are not exactly the same then there might be a big spark and an explosion as the highest voltage battery tries to quickly charge the lowest voltage battery without anything limiting the charging current.
Whether series or parallel, always use identical batteries. Not doing so can easily damage one or more of the batteries, especially if they're rechargeable.