I know I've seen this info before, but my Google-Fu is suffering today.
What's the recommended level of charge to store our
batteries?
The link in zoiDman's post has some really good info in it. Read it and you'll get a lot more than voltage recommendations. I store mine at room temperature at 3.7-3.75V. The page from Battery University suggests 3.8V. Cooler is better, but IMO don't go below about -10 deg C, so a typical consumer freezer would be good.
Does it vary with the different chemistries?
I use only hybrid Li-ion
batteries (Samsung 25R, LG HE2, AW 'IMR', Sony VTC series) and Li-po for model airplanes. All these are the same for this IMO.
How long do you go between charging to the optimal level and checking them?
Thanks for reminding me
I have two AW 18490 and one 18350 in storage for around 8 months, left at pretty close to 3.7V. All three are around 3.69 now.
I have two 2 1/2 year old blue no-name IMR 1600 mAh batteries I got with a kit that I put away after maybe 50 charge cycles probably in January 2013. I think I've cycled them twice since then and probably left them just over 3.8V the last time. They are still at 3.8V. I put these away when I was vaping at way lower power than I am now, just in case I might need them someday. I think I'll recycle them now
I've got 3 in rotation and 3 that have been stored for about 3 months. I don't want to ruin the stored ones or worse.
IMO the most important thing is not to store them full or empty, even for relatively short periods of time. I have eight batteries I cycle through on an ongoing basis. Three are typically in two mods, a Sigelei 150 that takes two batts and one in a mechanical mod.
With these I have a system. I place charged batteries in one spot and leave empty batteries in another. There are typically more empty batts than charged. I take batteries out at between 3.6-3.7V so they are at optimal storage voltage and place them on the left in the empty batt place. When another battery gets taken out of a mod I move the first to the right and place the new one on the left. As I need them I take them from the right side so they will all have about the same number of charge cycles on them over time. This means they will wear about the same and I don't have to worry so much about keeping them married when used in the Sigelei.
I try to charge batteries so they will not be sitting fully charged for too long, which for me means a day at most, but I aim for around a few hours. I don't stress if they go a day, but I try not to go longer than that and mostly that works out for me.
If I knew I was going to leave a battery for three months I would treat it as long term storage and be sure I left it at 3.7-3.75V.
