I have found my Lithium ebike batteries very good, long lasting and retaining very good capacity and range.
But I use my bikes all year round so the batteries are being used regularly. That said, the one on my Haibike can go around 4 weeks without being used and very occasionally longer. I store it in the house around 55% and it is holding up very well and will be six years old in March.
The thing not to do is to stop riding at the end of the summer, leaving your battery on the bike in a cold shed or garage and expect it to be fine in the spring.