THere's an SRN out form Moto that describes those scenarios. I do not have it handy. I believe the Impress battery may "lose" Impress functionality (battery gauge, Init, charge counter) functionality when not charged in an Impress charger. The battery will still charge fine and operate, just no Impress data going to an Impress radio. I think if you let it drain down then recharge in an Impress charger it will restore that functionality.
I was told by a Moto Impress product engineer that charging non-Impress batteries in an Impress charger will charge them a little better as the algorythms are better than standard chargers.
Also check your Impress charger firmware version. It should be labeled above the barcode, such as V3.4. Version 3.0 is known to have problems and can permanently kill the Impress communications functionality. Call your sales or service rep and they can get your chargers upgraded. The latest version is 3.4.