Hello,
today I've noticed that after the charging is complete (the green LED on the base and 100% LED on the charger are on) the charger stlll silently humms and voltage on the battery is 26,5 V.

I've installed four new replacement batteries prior to charging.
I never notice this before and can't find any info in the manual.

Is this some kind of charge that keeps the batteries topped up or this is abnormal?
What happens to the batteries when the are on constant charge like this?

Regards!