The longer version: Warranty Info Page
The plain language version:
All our LiFePO4 batteries come with a rock-solid 5-year warranty. If the battery fails for any reason, we will repair or replace it (at our option) with the same or larger capacity battery.
We do not pro-rate based on age of battery. Just a no-fuss warranty, same as we would expect if we were the customer!
Products other than our LiFePO4 batteries come with a 1-year warranty unless otherwise stated in the product description.