Rechargeable flashlight battery question??

[DaveTN]

I have three Fenix PD35’s 1000 Lumens, and a Streamlight ProTac HL 5-X USB 3500 lumens. All use 18650 rechargeable batteries. I use the PD35’s all the time, I have one on me and the others laying around. I charge them every couple on months and have never had one go dead. The Streamlight rarely get used unless I need to light up my whole yard, so I haven’t charged it as much.

Two months ago I went on a camping trip and charged them all. The Streamlight was dead, but I didn’t think much about it because it hadn’t been charged in probably three or four months. Yesterday I went to use it and it was dead again, hadn’t hardly been used in two months. I put the batteries on the charger and they showed 60-80%. I thought the light might be faulty, but I charged them overnight and it worked fine when I put them back in.

So I wonder what’s going on? Could it be that with 3500 lumens it requires nearly a full charge to even light the light? Or could the light be defective?

[peejman]

I'd guess the batteries have degraded due to lack of use. The lights usually have a min battery voltage threshold before they'll light. 

[RED333]

A chemical battery will develop a chemical bubble, the old NiCad batteries were notorious for it. If you did not completely discharge and then completely recharge would develop a chemical bubble and would only use that much of the battery. I am sure all chemical batteries have the same function lithium-ion is not near as susceptible to the chemical bubble but it does happen.

[DJTC45]

Like all batteries even the rechargeable type, and I've got a Fenix with a battery that charges with a USB port, and another Fenix that uses a charger. The one that uses a charger is probably 5yrs old and I recently had to buy one battery for it about 2 months ago. I don't use it as much as the other smaller one so I think that batteries shelf life just ran out. At least that's what I think.

[Prod951]

I use to manufacture lights for a few of the major brands the best practice when storing lights for long term is to fully charge the battery and turn the tail cap half a turn so the light will not function. 95% of the flashlights on the market still draw current like your cell phone when it's off.

[TennesseeCamper]

I have the HL-5 X also but I have not experienced the the battery problem.  It mostly sits charged up. Every once in a while I click it on and it lights up light like the sun.  
I keep the streamlight 18650 in a cheap Chinese eBay light and no issues with that one either. It gets used a little more often but it doesn’t seem to have any issues maintaining a charge. 
 

I have an old surefire G2 with a Malkoff led in it and another streamlight 18650 use it fairly often and it maintains a charge too.  
 

I wonder if you have a couple bad 18650s?

Edited May 26, 2021 by kentmck

[snorky18]

You may have a bad battery - they can show a reasonable voltage (60-80% charged as you put it) at rest, then as soon as you put any load on them at all, the battery falls on it's face and voltage drops to nearly zero.