You've said this before. My Sonicares have lasted from
two to four years.And that's buying them in pairs at Costco.

You must be recharging them in a way I am not. How often
do you drop them back on the charger?

In the instructions for my Oral-B's, there is an admonition to
totally drain the battery and then recharge: every six months for
the "1000"s that I just bought and monthly for the "Vitality"
that recently died.

That assumes the user recharges after every use, presumably creating a
"memory".

I tend to run my Oral-Bs down before recharging them. It's the Sonicares
that have had a seemingly too-short life.