Reverse charge protection for parallel primary lithium cells (CR2450)

Question

First time poster, long time follower here.

I am looking into the safety aspect of using primary lithium cells in parallel. The reason behind using parallel cells is to increase overall capacity. In an ideal world the two cells would be the exact same voltage and capacity, in this case there would not be a problem:

^{simulate this circuit – Schematic created using CircuitLab}

The problem comes when partially or fully discharged batteries are mixed with new batteries, thus creating a situation where the discharged cell could be reverse charged by the new cell. This is a big "no no" for primary lithium cells and could result in explosion. BAT1 in this case is the discharged cell:

^{simulate this circuit}

I need to put some form of protection for the cells. I cannot use series diodes like in the circuit below due to and unacceptable voltage drop (the cut-off for my circuit is 2.2v and it needs to last a couple of years!):

^{simulate this circuit}

I looked at using a PMOS configuration as posted at Protect lithium battery in parallel although this seems to only protect for reverse polarity i.e connecting the cell the wrong way round, not reverse charge between cells.

Are there any other ways of protecting the cells from being reversed charged ?

Answer 1

Here is a solution for you.

Schematics with a comparators. Use it.