Join Date: Aug 2006
Location: Arlington, VA
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Yep,time for an upgrade. And, not just because you leave the frig running.
What kills batteries most of the time is failure to maintain a full charge. However, there are other things which will greatly reduce battery life, including contamination, stratification, sulfation even if float charge is maintained but battery isn't exercised and/or equalized, etc., etc.
Investment in new batteries isn't cheap. Since you're gonna do it, you might as well get a good multi-stage charger to maintain them.
If you have a diesel boat, my suggestion would be to look into the Iota line of chargers with the smart IQ-4 regulator (either built-in or external..they come both ways). These chargers use pulse technology and have lots of other design factors which make them exceptional in maintaining your batteries, including "automatic equalization", high tolerance for voltage and frequency shifts, excellent RFI suppression, etc. Best of all, they are priced right, and come in sizes from about 90 amps down to about 15 amps. You can find them on eBay and elsewhere.