Deep cycle batteries

One of the biggest favors you can do for your battery(I'd buy the biggest deep cycle 12v Walmart sells) is to buy one of the better battery tenders. As a motorcycle rider this is a common topic that comes up when storing them. There are several brands but don't make assumptions based on whats familiar. I ruined a pricey trolling motor via a Sears DieHard tender several years back after it cooked my new battery! I use CTEK and Battery Tender for my cycles and farm tractor=bunches of them. There a few others that are also good. Avoid cheapo stuff from Walmart or any other bargain brands, like Harbor Freight-batteries are too expensive to overcharge! You need a smart charging type tender!!!
It's easy to hook up two 12v batteries-google is your friend and all you need is a some heavy cables from a salvage yard (the friendly kind that allows stuff they never sell to go cheap) You'll need to solder or crimp heavy terminal ends after cutting to length for wiring set-up.

Originally posted by Happy Tripping I am afraid that I killed my dealer-provided deep cycle/marine battery by using it instead of shore power. I put the cables on with the wrong polarity and the fuses blew without me knowing it. That night the trailer lights suddenly became very dim.

If I follow your explanation your battery is probably OK. The reverse polarity fuses are there to protect the converter and they've done their job. You ran the battery down once, which decreased its life, but not killed it. Replace the fuses and let it recharge from the converter for 24 hours and try it again. After disconnecting shore power and letting the battery sit for several hours with no load on it, the voltage should be 12.6-12.7. If so it's probably OK. Repeated discharges or prolonged discharged periods will decrease battery life, but once is not the end. That said, we all recommend dual 6V golfers if you plan to do any off grid camping. It's not at all complicated.

We have had 2 12v group 24 deep cycle marine batteries on our 177 for 5 years, now beginning our 6th year.  Even last fall when we were at RMNP and using our furnace a lot (temps in the mid to upper 30's at night, we would still easily get 3 - 4 days out of each battery before it got to 1/3 of a charge and I would have to change over to the other one.  So in essence we easily get 1 full week out of both our batteries even after 5 years.