Would a 270 amp alt, a D3400 up front, and 2 D3100s be okay for about 4500wrms? If my voltage regulator is set to 14.7 volts, how much drop would you expect?
WE can't actually see the DMM so maybe you hooked it up wrong or there's some other issue. One of the things we can see is the fuse rating, so that's why were using it.
I would go with XS. They have a faster charge, faster discharge, easier on alternator (~10 amperes per battery), takes up less space, and is made for car audio.