Hi
Even new dry charged batteries only have a limmited shelf life, a battery that has been used and drained out has already had some of its charge discharge cycles, and the time it can be stored will be very reduced.
Jet Skis come with dry charged batteries and we were advised to fill and charge them within 3 months of receiving them.
If you read back through some of the earlier postings on this site you will most likely find all the answers you need.
Brian