Davis Vantage Pro2 ISS Battery Life

Probably a dumb question… these batteries do not appear to be re-chargable… does the Vantage Pro not recharge the batteries with the solar? Does it just use the solar when it can, and the battery the rest of the time?

I’ve had the same battery in my Vantage Pro for at least 10 years… how is that possible if the battery is not re-charging?

Thanks!