Connecting Batteries in Parallel without Cross Discharge

The described circuit method of connecting batteries in parallel not only charges and discharges them uniformly across common sources, it also completely isolates them inhibiting any cross-discharging possibility. The idea was requested by Mr. Ron.


The Request

I found your site and it is most impressive.

I hope that you may  have a solution to the following problem.

I have two 12 volt batteries in my caravan and for charging  or providing power to appliances, they are wired in parallel.

I have been told that if one battery was to drop a cell then the healthy one will attempt to charge the bad one due to variation in voltage. The battery with the dropped cell is useless and in the scenario I gave, the healthy battery will not remain healthy for very  long. Is there a solution that keeps the batteries in parallel for charging and discharge in normal use, but separates them in a fault situation?  

Would appreciate any advice that you can give.

Ron

Circuit Description

The shown method of connecting batteries in parallel without cross discharge is very simple and involves the use a few diodes.

The diodes effectively block the inter links between the batteries preventing any possibility of cross discharge, yet allows them to charge from a common source and discharge uniformly across a common load.

Although the diodes provide an easy alternative for the above actions, it drops around 0.7V across itself.

The above drop might look insignificant, however during critical situations the issue could make a lot of difference.

In order to make the circuit more efficient a mosfet equivalent circuit could be wired up as shown, replacing each of the diodes.

The resistor could be anything between 50 and 470 ohms, the mosfets should be a P-channel type with voltage and current rating slightly above the max specified limits.

The mosfet option provides identical features like diodes with an exception that it won't drop anything critical.

Charging lead acid batteries in parallel with simple current control indicator feature:

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