Addendum:
The problem seems to be caused by the charger. The new chargers try to charge with more current so that it works faster. The Varia cannot cope with this. With an old charger it now works perfectly again. :-)

Hello dbieri
I have had the Garmin for 3 years and never had a problem with the battery. The best thing to do is never charge it 100%, this will prolong its life. Poss. apply for warranty.