Battery charging

[Dudley Smith]

My car has a substantial double pole master switch isolating both batteries. They are readily available , such as this one:
https://www.autoelectricsupplies.co....-pole-isolator
They are also used in boats, so there are lots of marine ones.

[dick campbell]

A point on your ignition being fed from only one battery. It does when the batteries are in series for 24v starting but as soon as the starter button is released then both batteries are switched to being in parallel and both get charged. One battery does tend to get charged more that the other which is more to do with the crude third brush charging control…..

[dick campbell]

I have 0.4 volts across the socket with the batteries turned off. I wouldn’t worry, you have not found a way of making free electricity. Some meters will induce a voltage, some digital meters are too sensitive. Put your meter back on and turn the headlight switch on and I bet your 0.25v will disappear, or use a non digital one, I did and no reading. Might also be coming from the dynamotor. It has some residual magnetism, which is why it is self exciting, and probably with all of the copper and the iron pole pieces could have some low voltage and very low current potential. Maybe someone on here has a more expert opinion.
Separate your batteries for charging but I don’t think that it is really necessary.
I intend to devise a way of disconnecting both battery earths. Like you I have a cut out switch to isolate 12v from the car wiring but a bigger issue is if the 12/24v solenoid sticks in, as there is no quick way to disconnect the batteries to stop the dynamotor being energised.

[Dudley Smith]

A further thought on this subject is that when starting, 24v is provided by both batteries but the 12v needed for ignition and solenoid comes from only one of the batteries. So over a long period of use one battery will be run down more than the other. Perhaps it is good practice to occasionally put the smart charger on each battery separately.

[Dudley Smith]

Thanks, Dick. My only concern is that the battery master switch has to remain on, whereas I prefer to turn it off when garaging the car.
Curiously, when the master switch is off there is still about a quarter of a volt across the dashboard socket. Where does this come from? Is it perhaps that in this damp weather there is a small amount of leakage across the master switch?

[dick campbell]

I use the dashboard socket and a battery charger/ maintaining charger. It charges and then monitors the battery providing a very low current just to maintain a fully charged state. Just make sure you get the polarity right.

[Dudley Smith]

I like to be sure that the batteries are kept well charged while the car has little use during the winter.
It is a bit of a fag charging the two 12v batteries in my AV105. Is there a simple way of charging them both at the same time?
Would it be unwise to charge via the +/- power socket on the dashboard?

Dudley

[Dudley Smith]

The Dynostart on my AV105 is becoming increasingly sluggish. Despite two fairly new and well-charged batteries, it failed this morning to turn the engine...