Eleven

I usually charge them up and then don't worry about them. That hasn't been a problem for me for any device manufactured in the last 5 years or so.

I read that the "best" way to do it is to charge the battery up to about 75% and then stick it in the freezer. That's probably only good advice for things with removable batteries though.

If you're worried about the batteries committing seppuku when they get to low then just put something in your phone's calendar to remind yourself to check them once every 6 months or year and charge them up if they need it.

I charged both of them up and they seem fine. I'm amazed my Vita can take that abuse.

I've never worried about it, but my old iPhone 5s died within like 3 months of being stored. But now that I think about it, My iPhone 4 still holds a charge after basically being stored like that for a long time now (I dig it up like every other 6 months). Must have been a fluke.