In series current stays the same, in parallel voltage stays the same, so if u're after 24v 100ah, then hook 2 up in series, otherwise parallel will give u 12v 200ah
Just to add to this as well, note that when working out ups battery sizes for time you wish it to run for is not as straight forward as 100ah / current used. the current usage needs to be worked out at the same voltage as the battery is run at for that ah rating.
You also need to consider that the batteries shouldn't be run under 40% charge and so for a 100ah battery your really looking at 60ah of usage before you start damaging the battery.
Considerations also need to be made for how the battery was tested to get the ah rating, a battery that had a constant load of 1amp on it for 100hours is different to one that had 5amps on it for 20 hours, both batteries will be rated as a 100ah battery but the one tested on 5amps for 20hours will be 10-15% better if it got run at 1amp (hope that makes sense).
Also if a batter is tested for example at 5amps and it lasted 20hours (100ah rating) and you want to run equipment that use up 10amps it does not mean u get 10hours. It exponentially decreases the usable time with more current, so adding that extra 5amps will loose you around 10% of overall time. (so 100ah x .9 = 90ah) 90ah/10 = 9hours instead of the 10 you would be expecting.
This increase is greater and greater until max ah(W) is reached for a UPS which is also why at max W generally a UPS will say it holds it for 1-5min
Just to add to this as well, note that when working out ups battery sizes for time you wish it to run for is not as straight forward as 100ah / current used. the current usage needs to be worked out at the same voltage as the battery is run at for that ah rating.
You also need to consider that the batteries shouldn't be run under 40% charge and so for a 100ah battery your really looking at 60ah of usage before you start damaging the battery.
Considerations also need to be made for how the battery was tested to get the ah rating, a battery that had a constant load of 1amp on it for 100hours is different to one that had 5amps on it for 20 hours, both batteries will be rated as a 100ah battery but the one tested on 5amps for 20hours will be 10-15% better if it got run at 1amp (hope that makes sense).
Also if a batter is tested for example at 5amps and it lasted 20hours (100ah rating) and you want to run equipment that use up 10amps it does not mean u get 10hours. It exponentially decreases the usable time with more current, so adding that extra 5amps will loose you around 10% of overall time. (so 100ah x .9 = 90ah) 90ah/10 = 9hours instead of the 10 you would be expecting.
This increase is greater and greater until max ah(W) is reached for a UPS which is also why at max W generally a UPS will say it holds it for 1-5min
