I got one of these for Christmas last year (my sister ordered it from Amazon for me). Since the back of the light unit has a lighted switch/charge indicator, I figured it would be best to not leave the battery pack plugged in to the light for longer periods of time. But last week I forgot. With the weather and a sinus infection I didn't get to bike for a week and a half. So now, at the plug, I get 0 volts from the battery pack. That seems like an extreme amount of parasitic drain for a week and a half. I'm guessing a cell went bad, and I don't want to burn down my house (or my place of employment), so I'm pretty sure plugging this 4x 18650-looking battery pack in to the charger now would be, technically, a Really Bad Idea™
Any suggestions besides cutting the pack apart to see if I can salvage a cell or 3?
Just one cell going bad would not explain the whole pack reading 0V. If there is a protection circuit in the pack the cells might not actually be at 0V. To check for this, take the outside wrapping off and measure each cell voltage. If they are at ~2.5V or higher they are probably fine and you can try charging it to reset the protection circuit. I would monitor the cell voltages during charge to make sure they are balanced; I don’t know if there is a system in place to keep the cells balanced.
If all the cells are actually at 0V it is risky to charge. At too low voltages the copper current collector in Li ion cells can dissolve, then upon charge the copper can re deposit and cause an internal short.
KOBRA Waterproof 1200 Lumens Bike Light Kit with 6400 mAh Rechargeable Battery and Red Tail Light
Somehow I doubt the battery is actually 6400mAh. I would bet your 18650 is probably more like 700mAh if lucky.
I would suggest you get a quality 18650 (ebay and Amazon are probably bad places to try to do that)
Instead, look into a 3400 mAh 18650 from IMRBatteries or one of the other reputable vendors mentioned on this forum
I have a similar light and the pack is arranged 2s2p. So that 6400mAh is for two cells in parallel. It most likely is over rated, but might be good enough.
Yeah, I forgot to mention that. Previous measurements indicate that my battery pack is 2s2p. IIRC, it was about 8.2v fully charged.
And I wouldn’t be surprised at all if the capacity is wildly overrated.
I cut the wrapping off the battery pack. They’re still wired together (since I can’t un-solder them at work), but if read 6.3v. If I’m measuring what I think I’m measuring, that’s the whole pack (2s2p). So EasyB’s explanation (the protection circuit) for the 0v reading makes sense. That sounds safe to charge to me.
Unless someone stops me pretty soon, I’ll probably just try to charge it up for my commute home tonight.
see, this is the situation where i think i am ahead of the game? if i get a simple 4x18650 battery holder, wire it up how i want/need… and worry about packaging it for use. I can slap my laptop pulls in and out to my hearts content, and take extras with me if i think i will need them…. i can re-purpose it to work with any other device, too.
I wish i hadnt bought my large powerpack, i should have bought the “kit” you put your own cells into.
I was just thinking that myself. This pack just dangles from my top tube, so if it was slightly larger and heavier, it wouldn’t bother me at all. And it would be really nice if I could just test each individual cell at work. When this one does die, I’m replacing it with a kit so that the cells are individually accessible.
I’ve been trying to figure that out since EasyB suggesting monitoring the individual cells as they charge. I think I can probably check the voltage across each of the two parallel packs, but even that’s questionable since the charger/protection board is still in-circuit.
I’m open to suggestions, but I can’t figure out any way to do it with the connectors semi-permanently attached to the batteries. If I’m missing a clever trick, please inform me.
Maybe I'm not understanding, or maybe I'm not communicating clearly. Here's the top and bottom (take your pick) of my battery pack:
I can't figure out any way to measure the voltage on an individual cell in this configuration. But I would love to learn how, if there is a way without ripping the connectors off.
One of the parallel pairs was at 3.09v, the other was at 3.18v.
I plugged in the charger for a few seconds, then checked the voltage on the connector to the battery pack and got 6.3v where I had previously been getting 0v. So I put it on charge. That was earlier. I just disconnected the charger, and now both sets of 2p read 3.9v. I think I'm good to go.
Sounds like low voltage protection kicked in which reset when cpluhhed into a charger.
Test as you would a single cell. You will still get a reading. Just touch the probes to the anode and cathode, not the metal strip