Join Date: Apr 2009
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The Mystery of Schroedinger's Batteries
Are they dead or not dead? Right now I have evidence of both.
Hi all, I'm hoping you can help me diagnose a situation with my house bank. A couple months ago I bought a pair of 200AH maintenance free heavy duty batteries (not quite true deep cycle but close enough) that had been pulled off a swanky yacht after a year of service. The owner was revamping his whole electrical system and the yard workers let me have the batteries for a super cut rate.
When I hooked the set up to my boat they appeared to take a full charge and work fine, but during a recent weeklong trip I discovered that after an hour or so, the voltage would steadily and quickly drop down to ~8V when put under any kind of load. Since the heavy duty batteries didn't have screw posts I had put tighten-down terminal posts on the smooth pos/neg nubbins. Fearing a bad connection there, I checked for looseness but didn't see any issues. I also tried hooking my system up to just one of the batteries rather than as a parallel bank, but the problem persisted.
It was so bad that my running lights wouldn't even shine at full brightness, so we ended up needing to buy a new deep cycle battery in the middle of the trip. The replacement battery worked fine, so I figured I'd been sold a couple of duds.
Now this week I took the batteries to an auto shop and when they tested them under load, the guy claimed they were fine. What am I missing here?