battery float charging - line loss = fail

I have a Chinese battery charging control module (XH-M603) that I'm trying to use as a float charger for a 12v SLA battery. The problem I am having is that the module only works correctly when it is connected close to the battery using short leads. When I connect the module using 30ft of wire (which is how I intend to use it) the module doesn't couple with the battery correctly. It doesn't seem to be just a matter of voltage drop where I could adjust the modules voltage settings to allow for the loss from the wire - the module just doesn't link to the battery correctly using the long wire. The total resistance of the 30ft of wire is only about .6 ohms but that is enough R to confuse the module's sensing circuit.

I tried adding a capacitor close to the module and in parallel with the battery which didn't seem to help much (though probably not the right cap.) I'm thinking that putting another small 12v SLA battery close to the module and in parallel with the battery that is 30ft away could work. The module would charge the battery close to it and then that battery would float charge the battery farther away.

But.. is there a better, or simple way I can eliminate, or offset the effect of the long wire so that the module thinks it's close to the battery? I could buy a float charger of course ;) but I'm trying to do this with things I have lying around and learn something in the process. -Thanks

by operator_error
November 13, 2020
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