RV Battery

Hank MI wrote:
The ECM (engine control module) draws power all the time, ...

True, but the amount of "Keep Alive" power is very, very low. Could it drain a battery over a couple of months ? Probably.

+1 for Trik-L-Start

Thanks for all your help. Just ordered a battery disconnect from Amazon

what year and model RV, what engine and chassis

how long have you owned it

is this a sudden problem that just started {new battery going dead}

in many cases, the engine battery does not charge from shore power

but it sounds like you have a problem

in many cases, when something like this developed, it is in the starter circuit
bad starter relay or solenoid, sticky pitted contacts, creating a high resistance short/drain , on what should be an open circuit

You could add a "Trik-L-Start" or an "AMP-L_Start" to keep the engine battery charged from your onboard converter. A simple three wire connection is all that's needed. That would keep the ECM, clock, radio, and other settings intact.

I have one of these on one vehicle. Battery post disconnect
For others I just disconnect the connector to one of the battery posts.

Wouldn't it be nice if vehicles had amp hour counters on the battery so they could automatically disconnect at 75%?of full charge?

Take an electric multimeter and put it on maximum amp setting, which is usually 10 amps. Disconnect either lead from your house battery and put the meter leads on the battery and on the loose end of the cable. This will tell you how much power is being drawn from the battery. Anything over a few milliamps is going to drain your battery in a few days. Some coaches have electric mirror heaters that do not self cancel.

Ok Motor homes have two batteries as a rule (or two battery banks)
Engine and House (Chassis and House, or Main and Aux)

They also have a converter and an isolator

IF you are plugged into verified 30 amnps (AC will work on FAN in cold weather on COOL in hot weather not not select COOL in cold weather)

Then check the following in order

IF YOU HAVE AN INVERTER. The inverter display panel.. THEN the circuit breaker feeding it

IF NOT The ciruit breaker feeding the CONVerter
The Converter
Make sure Batteries are CONNETED (Aux and main both)

Finally

The Isolator.. Some have Bi-Direcitonal (BIRD Bi-direcional Isolator Relay Delay/Device) some have one way isolators (ENgine charges house house does NOT charge engine)

To test that. USE digital volt meter. Measure battery voltages .. Take notes

Plug in, come back in 2 hours and measure

12.6 FULL resting
13.6 FULL Charging (Float)

Assorted volteages while charging.

IF you get 13.6 on house but 12.x on chassis. ADD Trick-L-Start.

The ECM (engine control module) draws power all the time, unless you have a chassis battery disconnect switch. Our MH, like yours I guess, only charges the coach batteries when plugged in to shore power and no chassis battery disconnect. Disconnect the negative cable on the chassis battery or get a Trik L Start, Amp L start that will charge the chassis battery from the coach batteries when on shore power.

its anybodies guess as to how the battery systems were actually installed, or what kind of devices it has...

is there a battery shut off switch on both the coach and the house batteries? does it have a battery "combiner" switch?
does the coach have a security or anti-theft system installed?
are there any aftermarket components that may have been wired into the wrong circuit?
or compartment lights or step light that may be staying on?....

there are many reasons for a battery drain and its usually something simple that someone has overlooked....