By Chris Dougherty
Chris Dougherty is a certified RV technician. Here is a letter he received about an engine battery from a reader while he was serving as RVtravel.com’s technical editor.
Why does my under-the-hood engine battery keep going dead when I am hooked up to an electric post at campgrounds? I have a Class C Jayco 32-foot motorhome with a V-10 450 gas engine. Funny thing also, I find this out when my propane detector starts screaming. It is wired to the engine battery, too. Oh, and there is a metal bar on the battery that I can lift up to disconnect the power to the one post or leave down and connected. Not sure what that is for; heard lots of opinions. —GiGi
Well, let’s answer these one at a time.
The reason your battery goes dead is that it’s not connected to the coach battery’s charging circuit from the factory, and isn’t most of the time. It is a requirement from the chassis manufacturer that the two 12-volt DC electrical systems remain independent. For this reason, the chassis battery can go dead, especially if there are “parasitic” loads attached to that battery like detectors, steps, stereos and generator start circuits.
The knife blade switch was probably installed to disconnect the battery to keep it from discharging when the coach is not in use. While I’m not sure where you live, another frequent issue is that when the battery is discharged in storage and the outside temperature falls below freezing, the battery is frozen solid and destroyed and will never charge properly again.
The fix for these issues with the engine battery
• Make sure you have a good battery. Many auto parts stores and battery distributors can test it for you.
• Install a built-in battery charging system like the Xantrex Digital Echo Charge, which will automatically transfer battery charging power from the coach battery to the chassis battery while the coach is plugged into shore power, keeping that battery up in addition to the coach battery.
• For prolonged periods in storage, disconnecting the batteries is always a good idea, and if it’s a freezing environment, removing them altogether and storing them in a warm location is best.
RVelectricity – 12-volt battery dangers (Warning: graphic content)