Battery Disconnect Confusion

DesertHiker wrote:

Krusty wrote:
I would try to figure out what is drawing the battery down and fix that. ie: If you have a dome lamp switch on the dash that controls a dome lamp that has its own remote switch, make sure the dash switch is not left in the on position.

How can I do this?

To check this remove the negative cable from your battery, set your multimeter to 10 amps and measure the amp reading between the negative cable and negative post. A reading of greater than 1 amp is too much parasitic draw and will drain your battery. Mine will read about .4 amps and will take weeks to draw down to 80% SOC. ECM as Bud stated and some other things will contribute to this draw. If the MH will not be used for several months just disconnect the neg cable and the parasitic draw is eliminated. You should never have to recharge your chassis battery for two weeks of camping but if you do when you run your genset to charge your house batteries put your key in the on position and your chassis battery will charge at the same time your house batteries are being charged. Once you measure what your parasitic draw is post it here and you will get help to find what is drawing your battery down.

So no warranty?
Meaning it’s an ex rental or super high miles?
Bad diodes in alternators seem to be a Ford thing. Never heard of it before except our sons 06 Mustang. Low miles 40 something on it.
Bad diode was causing a cam pos sensor code. Had alt rebuilt, fixed the otherwise seemingly un diagnosable code and running issues.

Do you have an electric step with light? You may need to shut off step by entry to kill the light.

Ah yes, these are good comments. Unfortunately, it was drained in something less than 9 days! Sigh. I am not having fun yet with this new motorhome.

enblethen wrote:
The chassis battery is drained by the computer (ECM). There is nothing that can be done to stop this besides disconnecting the battery or installing small charger to it.

I'm not debating your post, I'm not a mechanic but I think its a very low draw. It seems to take a lot of time to do that. The knife blade is a good idea long term IMO .

My only reason for thinking that is that I park my 2018 Ford for 2 weeks multiple times during the winter, unplugged from shore power and my chassis battery has never dropped below 12.5v.
I have it on a digital volt meter which I activate each time to view a reading.
I bought one of those 1.5 watt solar dash panels because my truck has a 'hot' 12v outlet to accept the little charge that panel offers. It maintains my chassis battery at 12.6v for the same 2 weeks or more period . That battery went from 12.5v to 12.6v's using that little panel.

Just an uneducated guess but if that tiny panel keeps a chassis battery topped off I would think the draw while parked is very low unless there is another underlying problem somewhere.
In the OP's case, a bad alt diode would not show up as a blown fuse anywhere but would cause a significant battery draw while parked as it was explained to me. Being that the alt will work fine while driving to charge the battery its in the parked mode where the problem might be, someone would never know there was a problem until there battery was dead from sitting parked. Just something to think about to try to help him resolve his problem.

RambleOnNW wrote:
On our moho the chassis battery also powers the electric steps. There is enough of a drain that I disconnect the chassis battery when not in use and regularly put a battery charger on it to top it up before doing the disconnect.

I discovered this by leaving the battery connected and with the various small loads plus the electric steps the chassis battery was drained in 30 days.

I am right there with you. That is my experience and solution with our 2007 Phoenix Cruiser on a 2007 Ford E350 chassis.

When out traveling, we don't stay in one place for 30 days without driving the rig, but the scenario is true at home.

I am not anal about it, but I recharge house and chassis batteries at home roughly every other month. The chassis battery is disconnected, the house batteries remain connected. They recharge to full fairly quickly which implies they are not suffering during extended non-use periods.

On our moho the chassis battery also powers the electric steps. There is enough of a drain that I disconnect the chassis battery when not in use and regularly put a battery charger on it to top it up before doing the disconnect.

I discovered this by leaving the battery connected and with the various small loads plus the electric steps the chassis battery was drained in 30 days.

^Yes, to an extent, but the OP never said how long it took to die.
But alluded to the fact that he was concerned about camping for a week or 2. So making preemptions off of a not so detailed description of the problem, I’d say it dies in a week. That is not normal parasitic discharge.

But who knows what the real story is. I cannot imagine a 2018 anything needing a “fix it guy”. Is it really out of warranty? Or is there more to the story like I first alluded.

People could get much more help, presuming that’s what they want or they’d keep their story to themselves, if they told the WHOLE story.

The chassis battery is drained by the computer (ECM). There is nothing that can be done to stop this besides disconnecting the battery or installing small charger to it.

Krusty wrote:
I would try to figure out what is drawing the battery down and fix that. ie: If you have a dome lamp switch on the dash that controls a dome lamp that has its own remote switch, make sure the dash switch is not left in the on position.

How can I do this?