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Ask Dave: My battery drains during storage. Can I disconnect a cable to prevent that?

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. Today he discusess what can cause an RV’s house batteries to discharge during storage.

Dear Dave,
I have a 2015 Coachmen Prism. It has two house batteries connected in parallel. After a week or two of sitting, the batteries discharge to 11 volts or so. Can I disconnect the batteries to slow down the discharge? If so, how many terminals do I disconnect? Thank you. —Kerry

Dear Kerry,
Thanks for the question. This is a common issue with batteries that are not maintained during storage. A deep cycle battery will naturally lose voltage during storage even without anything draining from it. But it typically doesn’t occur as fast as yours, so there is probably what we call a parasitic drain coming from something inside the rig. Usually, it is the LP leak detector, which can drain a battery down in 2-3 weeks. Or there might be something else drawing from it.

Searching for source of power drain from batteries

To find what it is, remove the negative cable from the battery and use a multimeter set to the amp draw setting. Place the red probe on the positive battery post and the black to the negative cable and see if there is a reading. If so, it means there is a drain. You can pull out a 12-volt fuse from the distribution panel until it goes to 0 and this will identify the component. It could be a radio that has preset channels or a carbon monoxide tester.

If you disconnect the negative battery cable during storage, it will disconnect everything but your battery will still drain down. If it gets below 11, it could freeze. Plus, it will sulfate and your battery will not be able to store energy as efficiently. The best thing you could do is to plug the unit in and maintain the batteries or use a solar panel maintainer. If you do not have access to electricity or a solar panel, this will not work and the next best thing is to remove the batteries and keep them in a garage with a maintainer.

Read more from Dave here

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Bob
1 month ago

The meter needs to be connected between the “lifted” cable and the corresponding battery terminal in series.
And lifting the negative cable will not allow the battery to drain from parasitic flow. Current flow inside the battery is from the positive terminal to the negative terminal. The flow in the circuit is actually from the negative back to the positive.
Lifting either wire will stop the flow.
“The direction of an electric current is by convention the direction in which a positive charge would move. Thus, the current in the external circuit is directed away from the positive terminal and toward the negative terminal of the battery. Electrons would actually move through the wires in the opposite direction.”

Larry Lee
1 month ago

Maybe try placing the red probe on the black cable and the black probe on the negative battery post to obtain a parasitic current reading.