For the record, my batteries are actually sealed lead-acid Hawker
Energy (Gates) Cyclon BC Cell (25 AH) and not cheap - but then they
are rock solid.

Same ones I use!
Floated across a switchmode 15A charger set to 13.8V.
Been in service for 6 or 7 years with no trouble.

I added an "aw ****" fuse at 60A between the middle terminals at the 6V
point, and it has a couple of hefty outputs ending in powerpoles.