charging circuit for series coin batteries
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



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.