Mine never seem to drop below the usual 2 full / 3rd flashing led after auto discharge.
I guess with another drone in use at times, the longest would be around 3 - 4 months for the Spark, but usually it's used every 2 - 3 months min.
(Luckily, our winter isn't severe and interfere as much as it would in the northern hemi.)
I usually just charge all 5
batteries up to full when going for a fly, using them in turn in the aircraft.
One is always in it, usually a full one from when flying last and changing over.
Then I use the charging station to top off that and the following 2 in line, the spare 2 in the normal charger.
I might fly 1, 2, 3
batteries to say 2 bars, and leave them, the others if unused will auto discharge, think mine are set for 5 days.
If I fly a
battery lower than 2 bars, I'll just fully charge when I get home and leave it to auto discharge as normal.
You could leave them on your charger (the 3
battery flymore charge base is handy for this) and every few months check them, if they go down to say 1 bar / 2nd flashing, then yes, drop them in for a full charge, then let them auto discharge.
Of course make sure it's your usual safe place for charging, under watch at all times, or outside, or in a fireproof location etc.
You could monitor them at intervals, and slip them out when the 3rd led starts flashing during a charge I guess, but to me using the auto discharge is easy and lets them have a full cycle.
If you haven't set the auto discharge days on each of your
batteries, then you can do this via the Go4 app
battery menu.
It'll be set from factory for 10 days, I think it might still have option for 2 days or upwards in there you can set.
I just chose 5 days in case I wanted to head out for a fly within that window.
If your
batteries start auto discharge AT ALL, they need to be recharged before use, otherwise cell balances can be off, which can lead to bad things happening in flight . . . like a
battery having a high SOC % reading for take off, but a very fast drain in real life.