Hey gang, I’m having a weird issue with my original BLF GT converted to BLF70. The carriers seem to be “picking on” one of the batteries and draining it down super low. I’ve gone through about 4 Samsung 30Qs over the past 6 months because the voltage on one of them drops down to ~3.0-3.5 volts while the rest are at 4.15-4.20v. Even after recharging the batteries, and leaving them alone on a shelf for a month, they go back to reading 3.5-3.6v.
I was storing them with both carriers full (8 batteries), and the lockout mode engaged. Killed a battery. So I emptied 1 carrier, put both carriers in with the tail cap loosened. Killed a battery. Now for whatever reason, the batteries that got “picked on” wont even hold a charge for more than a month before they dwindle down to 3.5-3.6v even just sitting on the shelf, not in a flashlight. I’ve tried both carriers and have had the same issue with each of them.
Sounds like they got overdischarged and are now internally shorted, or otherwise damaged. I recommend safely disposing of them, and getting a new matched set for your GT70 (and keeping the old batteries for use in other lights)
Yea somehow they got seriously drained. Thankfully I caught them before it was too late. I’ve got some new Samsung 30Q’s on their way. Any idea if this is an issue with the BLF GT carrier? Or is this somewhat normal with batteries in parallel for a long time?
Does it happen with the same slot in each of the carriers? Does it happen with the carriers outside of the GT? Could it by chance be that the 30Qs were defective in the first place?
Seems you need to conduct some controlled experiments to determine the root cause.
I was going to go down that road of trying to figure out if it was a specific slot, but these Samsung’s aren’t cheap so I figured I would consult the experts before blowing $$$$ on a wild goose chase.
I just realized I have some cheap-o laptop pull batteries I could test overnight and see if there is any kind of a pattern.
Zoulas, normally I have the carriers in the light, with the tailcap almost off (about 2 threads screwed on). I’m going to load up both carriers tonight, outside of the light, and see if there are any clues as to which carrier is having an issue… Or if it’s just the batteries themselves.
I don’t know about that being normal self-discharge. I have a bunch of 18650’s in my earthquake supplies that seemingly haven’t dropped in the 4 years that they’ve been packed away. I check them every 6 months and they seem to be doing fine.
Alright, laptop pulls got some last minute solder blobs on top, checked voltages and resistance on the Sky RC charger, and they’re in the carriers. I labeled them 1-8. All the internal resistances measured less than 200mO each, and all the resting voltages were around 4.15-4.17v. I’ll check them again in 24 hours and see if there is any kind of big difference, or if I need to let them sit for longer.
I suspect it is that particular battery issue. I have almost 4 old used 18650 batteries dropped to 1-3V by themselves (unconnected) this year. They are all from known brands like Panasonic, LG, Sony, and Vapcell companies.
24 hours later and there isn’t much difference between any of the cells. I put them in the light, screwed the tailcap on, and put it in lockout mode. I’ll check them again Monday night or Tuesday and see if there are any trends.
There’s some great advice already posted here by others. Here’s a long read if you’re interested.
I never leave cells inside any of my GT’s (or similar) to avoid the potential of what you are experiencing now.
Your GT is 4S2P cell config, which offers twice the potential of exposing weak cells. Even worse that the cell carrier with the higher net voltage will discharge into the carrier with the lower net voltage, putting further strain on the failing cell(s) as it discharges into them at an accelerated rate. It converts all the stored energy into heating the failing cell(s) in that carrier. Without a BMS to monitor the state of each cell and deactive the failing ones, you could ultimately be dealing with a potential frag grenade and/or fire bomb. As lithium cells age, they can create tiny internal shorts when lithium forms tiny tendrils across the poles. These are unpredictable as they can form and create a permanent dead short, or they can burn off. So a cell that self discharged before and no longer does is screaming at you to discard it now before its too late.
If you are unsure, its cheap insurance to discard the failing cell and relegate the other 7 for single celled flashlight use. Then buy a new matching set of recently manufactured, name brand cells of a currently respected model from a reliable know source. Dont skimp here and they will likely serve you well if you treat them properly. Charge and discharge them as a group so they will have a better chance of degrading evenly over time. Even better if they are relegated to 8 celled flashlights to assure an even aging process in the set. I never let my cells drop below 3.2V resting and store them at around 3.67V for long term.
I used to trade with a guy who’s business subcontracted for Sony Corp investigating all their catastrophic lithium cell failures. Among other exotic equipment, they owned 4 x multi million dollar scanning electron microscopes. Exploding cells happen far more often than people would ever suspect and usually go unreported. The ones reported to the manufacturers usually dont make the news and the device is quietly replaced. So its better to be safe than sorry. Especially while using a light that holds 8x18650’s in a sealed metal tube (think antipersonnel fragmentation bomb).
Just FYI, if your battery tube ever starts to heat up at an alarming rate, throw it in a safe direction ASAP and stay clear. If explosive venting should occur, avoid breathing the highly toxic fumes and dont use water to put it out. I went though this with a C8 several years ago that I had mounted on my bicycle handlebars. The cell tube burned my hand so I grabbed the light by the head and tossed it. After about 30 seconds, the lens shattered with a loud pop and smoke poured out for another 30 seconds. Thats when I decided to do some research about the tiny potential bombs used to power my lights! Then I recycled all my cheapo chinesium rewrapped cells and invested in the real deals.
I never thought about the series/parallel configuration making that issue worse… I think I’m going to start storing the batteries outside mine now too, even though I’ve not ever seen any of them reading lower than the others. Thanks
Update: I let them sit in the carrier for about 3 days and checked the voltage. All were just about the same as when I put them in. So I’d say the Samsung 30Qs I had in there just weren’t matched very well. Or one got damaged and started pulling on the others. I replaced a few as they were going bad (maybe 3 or 4 total).
So if anyone ever finds this thread and is having an issue with the BLF GT carrier draining a specific battery, your best bet is to replace all the batteries at the same time. Thank you to everyone who replied and helped!