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I am designing a circuit that will be powered by two rechargable coin cells in series, and I need to include a module to recharge them in-situ.

I have had a look on RS at the range of rechargable coin cells and it seems that there are two variations with regards to the chemistry; Lithium Vanadium Pentoxide and NiMH.

I am trying to determine suitable charging circuits for both types of batteries, bearing in mind that there are two cells in series. I am having trouble finding any example charging circuits, particularly for the Lithium Vanadium Pentoxide battery, which I am most concerned about as I know some types of Lithium battery require specific charging cycles.

What do these batteries require from a charging circuit?

Are there any things that must be avoided when charging these batteries?

Can you reference example charging circuits and/or charging IC's for these batteries?

Cheers!

Extension: I have also found lithium-ion coin cells that have a nominal voltage of 3V.

Please can you advice me how to design a charging circuit for a pair of these in series?

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Unlike charging circuits for Li-Poly batteries, for example, which require three stages of charging controlled by a special IC, charging VL-type Lithium Vanadium Pentoxide batteries can be done by fairly simple circuits not needing an IC since they are require only a constant voltage.

Here are three such circuits from the section on Vanadium Pentoxide Lithium Coin Type Batteries (VL series) from Chapter 3 of the document Rechargeable Coin Type Lithium Batteries

enter image description here

There are several more such circuits, including component values for each of the circuits.

The specifications recommend that

Charge voltage: 3.4V ± 0.15V

Charge current: For a battery voltage of 3V
    VL621 Approx. 0.2 mA or below
    VL1216, VL1220 Approx. 0.5 mA or below
    VL2020 Approx. 1.5 mA or below
    VL2320, VL2330 Approx. 2.0 mA or below
    VL3032 Approx. 4.0 mA or below

Note: There is nothing in the document re charging two cells in series, only in parallel.

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