You must have one of these first before you can do anything sensible about your batteries. Not optional---an absolute must have.
https://www.canadiantire.ca/en/pdp/motomaster-battery-hydrometer-0113010p.htmlAs for charging equipment, you can meet all possible needs with this converter/charger that has adjustable voltage. That means you can do the charging profiles recommended for your batteries no matter what they call for.
You can't do that with an ordinary converter or charger. The user manual (see link) explains how to operate it. You have to fiddle with a small screwdriver and a flashlight to set the voltage pot with a voltmeter attached. No big deal, but it is not a hands off gizmo--you have to be willing to put some time and effort into it. :)
The 60 amp size will do for a pair of 6s and will run on a 2000w gen. Higher amp sizes won't, needing more gen.
https://powermaxconverters.com/product/pm3-12v-series/
