Battery isolator charge vehicle battery on shore power

Thanks for the responses, greatly appreciated.

Upon checking this is a diode type unit and does not and is not suppose to charge the vehicle battery from shore power. I assumed it did and even though sitting for a while it has never failed to start, luck I guess.

My 94 Toyota had the old fashioned Cole Herse isolator, looked like a Ford stater solenoid. I added a switch to connect the house side to the vehicle battery and turned it on when on shore power. Can I add a simple switch and wires
to this isolator to connect batteries when on shore power?

First. Battery "isolators" are old school. With modern vehicle charging systems, you will never be able to achieve 100% SOC on your house battery bank no matter what size wire you use.

Get rid of your isolator and replace it with a DC-DC charger. No, this will not charge you vehicle battery. Go buy an inexpensive battery tender or carry jumper cables that can go from your house battery bank to your vehicle starting battery or buy one of those hand held battery boosters.

When I had a Winnebago Class C motorhome, the chassis battery did not charge when plugged into the pedestal. After killing one chassis battery, I installed a Trik-L-Start to remedy that. I never had another problem with it. While that particular product appears to no longer be available, something similar should be.

Ok now the isolator is either a diode block (3 large posts one small and cooling fins) or a Solenoid (2 large posts two small ones)

First case: Diode iosolator: A diode is like a check valve on a water line. Current flows one way (The arrow points towards NEGATIVE or in this case the batteries) and the short charger cannot push power into the chassis battery.> Thankfully these are kind of rare.. though I have used them.

For the Solenoid... That's not the part that controls itself.. There is some means of controlling the solenoid.. Some are controlled by the alternator (If it's outputting the solenoid pulls in and charges) Most today are controlled by a computer... If it's the ECC (Engine Control Computer) than no.. there is no reverse charge

If it's an Intelletec Battery Control system or other type of B.I.R.D. (Bidirectional Isolator Relay Device) then yes.

How to tell the difference.

After a period of NOT PLUGGED IN (even 30 minutes to an hour will do)

Method 1: Turn on lights..then plug in and if say 1-5 minutes the lights brighten (I mean VEHICLE lights by the way) It's Bi-Directional

Method 2: (Better) Hook up digital voltmeter to a "Vehicle" test point.. You may have a fuse block under the dash or the battery itself.. NOTE voltage (Should be around 12.5 or 12.6) Now plug in and come back and see if it has gone up.. NOTE you may have to wait a short time (like 30min to an hour).. If it's now 13+ you have a Bi-Directional Isolator.


Method 3... IF the 12 volt accessory outlet in the dash is a "Chassis" device (often is) and hot with ignition off... There are plug in voltage indicators Some are digital Some are Multiple light...

Again if shore power charges the chassis. they will show an INCREASE if you plug in 30 minutes after shutting engine off.

I will save you some search time on that last option

https://www.amazon.com/Zeltauto-Cigarette-Lighter-Digital-Voltmeter/dp/B00VL9JZ0K/ref=asc_df_B00VL9JZ0K/?tag=hyprod-20&linkCode=df0&hvadid=312064685033&hvpos=&hvnetw=g&hvrand=15882270661183137423&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9017021&hvtargid=pla-568712381669&psc=1

Most battery isolators charge both battery banks from the alternator when the engine is running.

Pretty easy to put your digital voltmeter on it and see whether it charges when the engine is running and/or when on shore power.

Yes, there are some battery combiners that will charge both banks anytime voltage is about a set level (indicating some charging source is on).

And, with any 19 year old vehicle, I would not ASSUME!

I don’t know much about Cs but I wouldn’t think it typical
to charge the start battery off the RV converter.
Is it a voltage sensing isolator?
That latches and charges house battery when it sees charging voltage
from the vehicle. (IE vehicle running). Seems more plausible.