Samsung 30Q batteries degraded?

I have a Thrunite TN40s which is a light with 4 XP-L Hi emitters running off of a 2S2P battery carrier. I bought 4 new 30q batteries to use in this light and they have not been used in any other lights. Due to my rotation of active lights these cells have not seen many cycles at all. Probably less than 10.

Recently the batteries ran out prematurely on a walk and so I put all the batteries in my Vapcell S4 and it appears that two of the cells were at approximately 80% and the other two were at 0%. This is pretty odd considering the age of the cells and the fact that I loosen the head from the tube to prevent parasitic drain when I won’t be using the light right away. One of the low cells has a relatively high internal resistance now of about 100 ohms. Both low cells had higher resistance than I remembered any of them having. On the bright side, neither had dropped below a charge of 2.5 volts.

Do you think those batteries are dying or is there something else at play here that I am not aware of?

I am not entirely sure, but find it interesting that exactly 2/4 of the cells failed, while the battery carrier is in a 2S2P configuration. The numbers are suggestive of the battery carrier or light being the cause of the failure. Do you happen to remember if the two failed cells were connected in series?

I thought that was interesting too but wasn’t sure what it implied. The battery carrier doesn’t seem very complex and has not seen much use. Unfortunately, I do not remember what positions in the carrier the batteries occupied.

I just thought of this while typing, what if the springs sagged to a point where one battery was not touching both terminals in its carrier slot? Would this have any negative repercussions?

If one cell was not in the circuit that could mean the other two would have been doing all the work while the other 2 sat there not being used at all.

Oh that’s a good point! It didn’t occur to me that the reason the other two were almost full is because they were not being used. I was assuming they discharged while the light was idle. Thanks for the insight.

I’ll take the light out again tonight and test the cells directly afterwards.

Yeah, that can happen in lights. Happens to my EA8 (The Cave Man) quite often. No carrier, takes 8 AAs, can run on 4 or 8, one side has consistent contact whereas the other one can “flicker” or even not make contact ’til bonked.

In actual use with 4, I just use the good-contact side.

In actual use with 8, there’s no interruption, but even if contact is broken, another bonk that makes contact again, the 2 sides will “even out”.

Don’t think I ever had the dodgy side actually “fail”, but if that happens, yeah, the result would be 2 spent and 2 unused.

I suggest try putting new, good batts in the carrier then into the light.

Mark each cell and take out once a week and write voltage reading on a piece of paper.

Long process though but eliminates other variables fast.

but the readings would depend on the use of the light, that week


4 new matched cells, run on medium until depleted. Check cells to see if all of them are depleted, or if it was just using one of the parallel banks.

Sorry, no update yet. I was so exhausted last night that I went to bed early. I almost never go to bed early!

Anyway, I will start by testing with the four cells I have already since they both charged back up to 100%. As long as they haven’t self-discharged since I did that, I think I should be able to see a pattern by recording their discharge rate and which slots of the carrier they are in. I would hate to stress a new set of batteries like that unless I have to.

Oh, I forgot to specify an obvious thing NOT to use the light! Sorry…

Where did you get the cells? Any chance they’re fake 30Q’s?

I believe they are from 18650batterystore.

So update, before taking the light out last night I checked the batteries and two of them had somehow discharged more than the other two, just from sitting in the light idle. I charged them all back to 100% last night and they are sitting outside of the carrier from then until this evening to see if they self discharge while outside of the carrier. I suspect the carrier may be to blame because one of the high-resistance cells from before was not one of the two with a low charge this time. It would appear that it got in one of the “good” slots.

Another update, I got preoccupied and left these in the flashlight for an extended period of time. Now two of the batteries seem to have died. (Mea culpa)

When I put the dead cells in a charger they are detected as NiMH and when I put them in a D4V2 it does not function at all. The most significant finding is that the ones that died do not match the trend in self discharge from the data I recorded earlier. In other words, it wasn’t necessarily the worst cells that died. One of the ones that died was one that displayed no self discharge previously. This leads me to conclude that the carrier in this flashlight is almost definitely compromised in some way.

I have a set of Sanyo 18650GA cells that I will be swapping in this week to confirm if the light or the carrier is really discharging cells. These red 18650GA cells are currently troopers that maintain their full charge for weeks at a time. It should be obvious if they start having “self” discharge problems.