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Ask Dave: How can I charge my engine battery when connected to shore power?

Dear Dave,
My converter, Progressive Dynamics PD9130V Inteli-Power, only charges the two 6v lead acid, deep cycle house batteries. I wish it would charge both the house and chassis batteries. Are there any negative issues connecting a 3-amp Battery Tender to a 110v outlet on the RV to keep the chassis battery charged while the RV is connected to shore power? —Pablo, 2002 Fleetwood Bounder 31W

Dear Pablo,
I do not know of any RV chassis manufacturer that would recommend or allow a charge coming from a campground source through the converter to charge your engine battery. First, you have the electrical surges from a campground pedestal that can wipe out most of the electronics in an RV, not to mention the engine alternator, electronic components, and the engine computer.

Your unit most likely has a converter that will provide a 13.6-volt charge when the batteries are low and then drops to a 13.2-volt charge as a maintenance stage. However, if you have a large inverter or solar charging system, it might have a multi-stage charge. That would throw 16 volts as an initial bulk stage charge to break up sulfation which would not be good for your engine battery and electronics.

Charge the house batteries while you drive

Your unit should have a Battery Isolation Manager solenoid (BIM) that provides a charge from the engine alternator to the house batteries while you are driving. There should be a switch on the dash that also allows you to provide a jump start to the engine battery from the house batteries. This is a spring-loaded switch, as it can only be a temporary jump.

Using a trickle charger

As for the second part of your question, yes, it is OK to use a trickle charger such as the Battery Tender (or, my choice is the Battery Minder) plugged into either an outlet inside the rig or, better yet, plugged into the 20-amp residential outlet on the campground pedestal. It is typically easier to run an extension cord from the pedestal under the rig and up into the battery compartment.

Your rig has the chassis battery either in the stepwell, which is open to allow venting, or up in the front engine compartment. Either way, you could permanently mount the device in the compartment and have an extension cord plug placed in an accessible location.

One last comment. Most motorhome batteries do not need a charge for the amount of time you are camping. Unless you are staying in one location for a very long period of time, an engine battery in good condition should stay charged for at least a couple of weeks.

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.

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Arnold
1 month ago

Inside our Ford E-350 a Battery Minder is connected to 120 V (when connected to shore power) and also plugged into the cigarette lighter inlet and this keeps the starting battery charged. This fortunately works as the cigarette lighters are “hot.”

David Solberg
1 month ago

I do apologize for my misrepresentation of the Battery Isolation Manager (BIM) as I have been wrong for the past several years. At Winnebago we used a dual battery solenoid for years that did the charge from the engine charging system to the house batteries while driving and was only a spring loaded “jumper” to the chassis battery. My go to source for Winnebago information was the dealer technical trainer and in one of his “white papers” he sent me was a reference to a new solenoid called the BIM that owners were having issues with. It did not describe what the new solenoid did and I had assumed it was an electronic or “smart” version of the old solenoid and would shut off the power once the house batteries where charged so it would not boil the lead acid batteries at the 14-volt contant charge the alternator could put out. It does that, however I did not see the info on the ability to charge the chassis battery in the other direction. I did some heavy research and learned something.

Drew
1 month ago

I bought an inexpensive Trkl-Start that connects the house batts to the chassis batt. It keeps the chassis one charged by directing a small amount of d/c to the chassis batt whenever I’m on shore power or generator. It’s worked for 10 years with no problem.

DAVE TELENKO
1 month ago

Its Dave’s BIM statement thats wrong!
Found this & its confusing on how it works! Its the last sentence thats confusing in regard to the rest of the statement!

The Battery Isolation Manager isolates the two battery systems, Chassis & Coach, in a Motorhome. This prevents loads in one system from discharging both. It also connects the two battery systems together during charging. Both batteries are charged if either is being charged. The Coach Battery is charged while driving down the road, and the Chassis Battery is charged while plugged into Shore Power at a camp ground.

Hmm, this is from  www.PrecisionCircuitsInc.com
Snoopy

Bob p
1 month ago

We had a 2002 Mountain Aire that the chassis battery would be low after 2 months sitting. I bought a 12V battery maintainer from Harbor Freight for less than $6 on sale. The 12V leads were long enough for me to connect to the battery and run through the engine compartment, under the “doghouse” seal and plug into an A/C outlet behind the copilot seat. It produced 3/4-1A and was enough to cover parasitic draws from the chassis battery. I never experienced a low or dead chassis battery again in the 4 years we owned it.

Don
1 month ago

Sorry Dave, but you really blew this one.
Most motor-homes, or at least the higher end rigs, have what’s called an echo charger. it senses the charge being sent to the house bank, and if the voltage is over 13v, it provides that same voltage to charge the chassis batteries. This is precisely what you “do not know of any RV chassis manufacturer that would recommend or allow a charge coming from a campground source through the converter to charge your engine battery.”
Maybe you should sub-contract electrical answers to Mike Sokol?

Dennis K
1 month ago
Reply to  Don

Totally agree Don. Dave really should have had Mike answer this one.
My Motorhomes have all had a BIRD (Bi-Directional Isolator Relay Delay) system that “When the vehicle is being driven, batteries will be charged from the engine’s alternator. When the vehicle is plugged into shore power, batteries will be charged from the converter or battery charger.”
I also have a 12v to 12v charger in my car trailer that maintains the trailer battery from the tow vehicle which could be setup either way.

KellyR
1 month ago
Reply to  Don

Hmmm. I guess I have a low end motor home because mine works like what Dave stated, as I asked the same questions of the manufacturer.

Rock & Tina
1 month ago

Dave, most modern motorhomes, “allow a charge coming from a campground source through the converter to charge your engine battery,” via a their Battery Isolation Manager.

TIM MCRAE
1 month ago
Reply to  Rock & Tina

Thank you for saying what I was thinking.

This answer is total nonsense! I am not going to even try and explain. Total nonsense.

Ok, yes, IF your rig does not charge your chassis battery you could run a battery minder from any AC source.

I would not leave it connected while the vehicle is operating. But I don’t know why, just because…

KellyR
1 month ago
Reply to  Rock & Tina

I guess the operative word is “most”, as my 2014 does not work that way.

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