Found these three East Penn documents filled with good info including temp compensation, why Sealed VRLA, AGM vs GEL and more.
East Penn, Deka & MK are all the same with different corporate brand names. Also many after-market auto store brands are identical to these.
I wish they could make an battery that can operate at 130 degrees with no harm,I only get about 2 to 3 years in my cars.
Steve
With lead batteries, the more pounds of lead, the more capacity. Plain and simple. I once built an electric car with 12 East Penn Deka gell 8G4DM marine deep cycle 130LB batteries, worth about $4,000. After about 20 deep discharges, capacity started to diminish. So, buy as much lead as you can handle and don't discharge beyond 50% discharge, or go with lithium.