Let’s say you buy 10 30Qs in 2021, then another 10 in 2022. Do you lump them all together or do you write the date on them? I know it makes sense to keep them separate but you will know when one goes bad so I am thinking it’s pointless. A new one or old one can go fail.
I guess it becomes more important to label them the longer the time between purchases.
I keep a hardcopy battery log journal. Multiple cell lights: I keep cells for that light grouped with a rubber band and pertinent information on a sticky note. Date, voltage, which light it/they are for.
I don't have many batteries. Most I have of one brand is 8 and the other brands are all pairs. The pairs I put a sticker on one but not the other. The 8 pieces I just number them. All go in their cases and then they all go in a plastic bin.
I mostly use 30Q’s and mark them with different color Sharpie markers and store them in the lights I use often only. The unused batteries are stored in a single plastic storage case. I inspect the batteries often because I purchased some EBL batteries ( before knowing better not to ) that have leaked a tiny bit, so they were scrapped.
Currently I own some four dozen 18650 cells, with only five different brands/types.
BT Cells I especially bought for use in multi cell lights stay with that particular light.
The rest of the cells are located IN a single cell light (ALL my lights are loaded).
When one of those lights runs low, I simply take the cell from an other single cell light.
Only two cells are stored in a box, in case I need to put an extension tube on a light.
When I buy/get more lights, I will buy more cells (probably 30Q’s).
I only group batteries that are used together in something like 3 in a flashlight or 2 in a vape-mod, those paired ones stay together all the time. Batteries that are used individually I store together like the VTC5’s and VTC6’s I use for vaping. My flashlights have a battery inside, I charge it when needed and put it back in when done, for I don’t believe in big storage of especially Li-ION batteries as they age just from lying around.
Any multi-cell lights get a matched set up front, and they never leave the light except when being charged. Never swapped, never mixed’n’matched, nothing. Cells are married to the light.
1-cell lights get whatever they want, as it doesn’t matter.
Cells that are kept for storage, I usually keep them by batch, and I’ll “use up” odd cells first (eg, good come-with rewraps, those with on-board charging, etc.) as needed.
Stored cells are pretty much SHTF cells, or for lights that don’t come with their own cells.