Rechargeable battery in a Phonak EasyCall II

I’ve got an EasyCall for my hearing aids.

Lately when charging it, it doesn’t turn green when finishing charging but when I check, it’s at 100%.

The battery also still lasts me a week on a single charge.

As it doesn’t turn green when finishing charging, does that mean my battery is failing?

I’ve never owned something where the battery has failed / failing.