Any problems allowing rechargeable batts to sit unused for many months?

I've got more than enough 18650s and AA/AAA NiMh batteries. The extras are stored in plastic battery cases inside of a Pelican case. But I also have flashlights that rarely, if ever get used, with batteries sitting inside of them. I do loosen the tail caps on my lights in order to break any electrical connection and avoid parasitic drain.

Most of my extra batts are sitting at 4.0v to 4.10v for Li Ion, and my NiMh batts were fully charged, so I'm sure they've lost a little charge.

Is there any advantage or disadvantage to allowing some rechargeable batteries to sit unused and rarely charged, compared with NiMh and Li Ion batteries that see regular use and somewhat regular charging? They are all 2.5 to 4 yrs old too.

Ideally store around 3.7v give/take if months/years, however its no big deal imho , just make sure the lights are locked out as you are doing. It will shorten their life a little, but probably unnoticeable unless counting the cycles. 2.5-4yrs is getting really towards the end of their best anyway.

Good question,I have been curious about this to.

todays rechargeables be they NiMH's. Li-ion etc can literally sit for a decade and still have more than half a full charge. Depends a LOT on the maker etc. My 2700mah Powerex AA NiMH's drain out so fast outside the light Im left scratching my head.

I have had an 18650 cel in a convoy M2 in my glove box for ages(years), check it every 6 months if not used, top off, sometimes 12m time, voltage barely drops 0.01 or 0.02v. Build up resistance, wont charge past 4v................dont care as still of use anyway. Worse case recycle and buy a new for £5 or so................

I will add i have some older 18650 cells from easy 5+ yrs back still charging to 4.19v and holding it, had 100+ cycles easy, some 300+

Well... Li-Ion batteries will age over time, regardless if used or not (though cycling does put extra wear on them). How fast they wear is dependent on the temperature and the state of charge they are being kept in. I don't think they have much self-discharge though, but can't really say much about it since I don't have any loose Li-Ion batteries which are not in use...

As for NiMh, it varies with the type of battery. LSD batteries as are now common should hold their charge for several years, I believe Eneloops even do so for decades... however, non-LSD cells do not so well.

Just for the record (and because it fits in here), this week I've performed my regular recharging of unused batteries. Unfortunately, it's been a year and 2 months since I last got around to it, and there are two NiCd cells from 1988 or 1989 which haven't survived this, they hold steady at 0V and refuse to hold any charge, so they will have to be recycled. All NiMh batteries were able to be recharged, though a few of them may have been heavily compromised, holding at a resting voltage of only 0.69 V prior to charging and filling up surprisingly fast (these are all non-LSD batteries). This is out of a total of 39 non-LSD cells (inlucind NiCd). On the other hand, there are some Eneloops where I decided that they don't need to be recharged yet.

The Li-Ion cells i'm not so sure about, some NiMH batteries do well in storage more than others. The LSD type seems to hold out better as they don't discharge as quickly. Eneloops do well in storage. Some people will cycle through their spare cells in the devices they use so all the cells get usage at some point.