Postcard RTK with Portability Shield: Battery voltage measurement error?

[amlago]

Postcard RTK with Portability Shield: Battery voltage measurement error?

When I charge the Postcard with the shield on, the voltage displayed goes from the usual 4.2 volts to 4.4 volts.
Is this normal or is the indicator faulty?
If I charge the battery with the shield off, the voltage is correct and does not exceed 4.2 volts.
I'm worried about damaging the battery if I charge with the shield on, which is the most practical way to do it in the field when connecting to a power bank.

Regards
Angel