Depends on how well you take care of those batteries!
Basically don't charge them to 100% not to use them and don't fly at less than 10%. If you know you won't be using batteries for a long time then charge them to around 50-60% and leave it. Keep them in a cool dry place.
Also look out for any swelling as it may indicate that the battery is no longer working well.
There was quite a bit of info on the A2 course I took on batteries. I'll dig up the info on there and share on here as it's been a while and can't remember exactly.
Just checked one of the slides from the course and they recommend that if you won't plan to fly for a while to keep batteries at between 40% and 50% of fll capacity. If you have a full battery that won't use, they recommend to drain it.