12.6 v is fully charged. Check for voltage drop between battery and starter.

Just commenting on what endeavor1 had "originally" with ground from engine to engine and back to one battery. Personally I've always had each engine ground to battery with a strap between engines as well as battery to battery. Grounds can be troublesome leading to failures on who knows what.

Agree ^^^^ I couldn't figure out the wording

I hate grounds!!! They always seem to cause me the most issues and are tough to track down. Over the years I'm getting better though. Ohm meters are my friend along with a wire wheel to clean up contact areas

kinda like an older rusty Michigan pick up truck with a snow plow issue. I just end up running grounds everywhere and problem solved. Lol.

Can you please explain the permanent magnet starters and whether or not they are plug and play? My SB engine spins slower than port and I plan on replacing the starter as a result when doing mani's/risers. . . Maybe a PM if you are kinda enough and don't want to hijack the thread.

I have 1 G27 Deka Deep and per Deka the full charge voltage is 12.5. Just bought a Duracell G27 Combo., full charged volts is 12.7. You have to check with the manufacturers data sheet for your batteries, they're not all the same.

I love them, much more cost efficient than replacing expensive components!

Read up on how to charge agm batteries,,,,,there different than lead acid

Yes these are still "belt driven air cleaners." Think I found my problem - had a ground that wasnt connected (my bad when I put in the new charger). I also rewired the battery switches - not quite sure what BT had in mind when they wired them . . .. thanks for all the help everyone!