I don't NEED the extra 3Ah's BUT it's nice to know, I have them there...
And the TS prismatics are SAFELY charged up to 3.8v.
(NO loss is "cycle capacity")
Yes, sometimes I use "all" of the AHs.. (Not really, because ("all" is) I discharge only to 2.8v whereas others will routinely discharge to 2.5v to 2.7v)
The only reason why I use "3 chargers", is because I already had them, and didn't really want to spend money on a 36v 15-20a charger.
Your charging habits and mine are relative..
Look at it this way...
You use 15 out of 20ah on a daily basis and then recharge.
I use 15 out of 60ah on a daily basis and don't have to recharge. 3 days later... Yes. So I do a recharge once every 3 days, while you do it every day..
So even though I MAY get less cycles, I will have the battery last longer than yours, given the same amount of "use".