I was always taught to bring them down to around 25%, and definitely not over 60% when expected to be unused for more than 1-3 weeks.
I've never experienced LiPos degrading (capacity/ max voltage wise) when brought down to 25% for storage, but perhaps 40% also offers the same sort of protection, and a little quicker to bring them back to life too if they don't need to charge so much when brought back into use.
When I joined to help, I was quite eager to introduce Colin to the LiPos, as he has been out of the robot combat scene for most of the LiPo introduction and rise phase, I managed to impress even myself with the weight difference, as i'd never really used or even held the old style batteries before, so didn't realise how large and heavy they were in person.
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