Well you said it all when you said "Magnatek 6345"
As converters go this is the basement and then some. there is no voltage regulation. or nearly so, the "Regulation" if you can call that is what is called a Ferroresonant or saturated core transformer.. IT's designed for 110-115 volt input not today's 120 volt standard and it simply can not control it's output.
It's a well known battery boiler/killer
Recommend a Progressive Dynamics 4655 to replace the rear part (The "Guts") of the 6345
Here is a link to the company web site. You can get one from most RV places or Best Converters
Replace it as soon as your budget permits. You will save the purchase price in better battery life & performance. There are kits available to replace the innards of your 6345 with a modern 3-stage switch-mode converter/charger.