I’ve been suspicious for a while about how hard my batteries for house are losing voltage over a ~ 12 hour day. I know the fridge compressor comes on periodically at 3 amps to keep the coolant moving around, but that doesn’t add up to taking a battery from fully charged to near fully discharged in 12 hours – 36 Ah of draw on a battery bank with nominally 200Ah of capacity wouldn’t drop my voltage from 12.8 to 12.1, and it’s not even 36 Ah because it’s not a constant draw.

Yesterday I split the house bank after charging it. Battery A was designated “no load”, and had all draw removed from it. It was still connected on the positive side with a cable to the charge splitter, but the negative was disconnected as was the paralleling positive. A read 13.03 right after charging (worst way to measure it).

Battery B had the house load connected. With some load on it after charging, the voltmeter declared 12.8 volts. I went to work for the day.

When I measured the battery states 12 hours later, battery B in the house bank was at 12.2. Battery A was at 12.0. I think it is safe to conclude that battery A is dead and needs replacing.

However, the story does not stop there. This morning I fired up the engine to charge battery B (since A is out of circuit until I replace it), and decided to check the charging voltages and amps. Off of the back of the alternator, the numbers were 18A and 14.18V. At the input side of the splitter, the voltage had fallen to 13.6, though the amps were constant. The feed after the fuse to the house bank registered 15A, at the same voltage.

The ProsplitR claims to be a 0.0 V splitter, and that certainly appears to be true. It also appears that it chews somewhere around an amp to do what it does when powered up. A 0.6 volt drop between the alternator and the splitter is not great though, and means I probably need to add yet more cable to the “replace this” list.

Battery investigations
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