Edit: well never mind, lol; but 3 batteries is better than 1 in this case. I just know the pros that are running the 24v or 36v lithiums, are running multiples of them in parallel.
Yes, they are running multiples of the "36V-in-one" battery module. The popular name 36V model is rated at a total energy supply of 2496 Watts. You can only get so much energy stored inside one box, and that's it. Compare that with a good 100AH 12V Li Iron Phosphate battery, and you see each carries around 1280 Watts. That's per battery, so 3X is 3,840 Watts, or 54% MORE stored energy than the single 36V energy cell provides. This is why pros run 2 of those 36V units in their boat.
One advantage of 12V batteries is that if one battery fails, you still have 2, and if you happen to run a Lowrance Ghost, you can reconfigure the wiring in a couple of minutes, then reprogram the Ghost to 24V, and save the day. If anything at all happens to the 36V model, you're done; there is no regroup beyond replacement.
If your special 36V charger dies, you're done. If you have 12V batteries, there are inexpensive chargers that will charge Li available as a backup. Or, if you have a 3 bank Li charger, you can swap leads after the first battery charges to get all 3 charged.
I could go on with arguments against 36V battery configurations, not to mention the inflated cost for that big-brand-name. I got 3 good batteries with more stored energy for a lot less than a single 36V unit would cost. I'll never own one as my choice.
BTW, hopalong is correct that Amp-Hours are not cumulative. Three 12V batteries rated at 60AH put into series makes a 36V 60AH system.
The pros using three 12V batteries are using 100AH batteries, not 60AH batteries. Likewise, those with 36V that I have seen are all using two of them - for the same reason other pros don't use the 12V 60AH.