sunshine_eggo
Happy Breffast!
A benefit of a 15S setup is lower cost. It's minor but a benefit nonetheless that reflects that natural tension in building batteries: more batteries offer more capacity but cost more.
Lower total cost, but higher per unit energy cost. Since a 15S BMS costs the same as a 16S BMS (especially if a universal is chosen)...
15S + BMS is more $/kWh than 16S+BMS
15S yields less kWh/$
Do you want to save money or get more for your money? I'm in the latter camp.
Furthermore, the 15S will have a reduced cycle life due to higher current and greater DoD for a given application than 16S. Not a lot, but one can't argue the opposite. This further increases the cost of the 15S...
As for 16S better matching 48 volt operating ranges, it seems that 15S will work fine with currently available equipment and are a better match for legacy gear that was used with FLA batteries.
literally the opposite of what has been said/documented.
15S operates 4.5V below the low limit and 4.45V under high limit of FLA.
16s operates 2.5V outside the low limit and 0.8V under high limit of FLA.
Less voltage is outside of FLA range with 16s than 15S. Not sure how 15S is a "better match."
I'm not a proponent of one over the other but I believe it's important that people aren't given the impression that 15S can't be part of a highly functional 48 volt system.
I am a proponent of 16S. It's literally all upside for 16S. I don't believe I have presented anything that can be used to give an impression that 15S can't be as you state. It absolutely can. It's just always second choice.
16S has some advantages just as 48 volt has advantages over 24 volt (but the 16S advantages over 15S are much smaller compared to 48v v 24v).
If there are no existing restrictions, there is no technical reason to select 15S over 16S. There may be a financial reason, but if $150/battery is where one is trying to save money, the system margins are probably too tight.
Now... all of that said... if I had an option where 15S was 25% cheaper per kWh than 16S, sure. I'd probably go for it, but I would wrestle with the decision.
Back to the OP... they have no choice. I wouldn't consider mixing 15S/16S, nor would I scrap or replace a perfectly healthy 15S with 16S just on principle.