Hi, I’m hoping someone can advise me:
I’m travelling and forgot my charger for 8.4v bike light battery pack (2x18650s in series with protection circuitry).
I have found a 9v 400mAh charger with matching connector (hoping polarity is the same).
Will this work to apply just a partial charge to the batteries or will even a partial charge damage them? I’m aware going over 8.4v is a very bad idea, but being a complete electrical illiterate I’m hoping you guys know better…?
It might work to partially charge, but I would NOT do it. If you forgot and left it on the charger, really really bad things could happen. I do not know if applying 9V for a few minutes would cause any damage.
I know lead acid batteries are charged at over the nominal voltage, but they’re not as sensitive as lithium chemistry batteries.
BTW, for reference, mA is the charging rate, mAh (mili Amp-hours) is the capacity. Chargers are rated in mA, cells/batteries in mAh and sometimes just Ah for things like car batteries.
Yes, you can do it but since you have to ask……you shouldn’t.
The things that can go wrong without some way to track the charge (which I’m sure you don’t have) are rather nasty. :Sp
Thanks for both your replies!
I do have a sort of method to check the charge: the light head has a three level led juice indicator in the switch (red>orange>green). I know it takes at least 3 hours to fully charge with the correct charger. If I try it for say 15 minute blocks (with alarm timer so I don’t forget) only until the indicator turns orange I’m hoping I can put a little juice in there…
What I think you have rightly reluctantly helped me confirm is that the reduced rate of charge (400mA) won’t damage the battery pack, but the duration when it reaches above 8.4v will…?
Sorry the battery pack is 6400mAh and the original charger was 1000mA.
You can use slightly over voltage (normal lithium charging is [constant current > constant voltage]). What you can’t do is “over capacity” it much.
That’s a very low rate of charge but since you are using a NiXX charger you really don’t know WHAT it’s putting out. NiXX over volts the cells to achieve charge, Lithium do not.
Is that 6400mAh known good cells or Chinese claimed capacity? If not verified in all probability the actual capacity is less to WAY less. Do the math: if the charger is 1000 and it charges in 3 hours that either indicates it was still half charged or it’s a 3000mAh cell.
A proper 8.4v li-ion charger does not simply apply 8.4v to charge the pack. Li-ion require a specific constant current then constant voltage (cc/cv) charge profile.
And you don’t even know if the polarity is correct! I wouldn’t even consider it.
They are Panasonic NCR18650Bs confirmed. My math is fuzzy, I’m guessing how long they usually take to charge - 3hrs was an absolute minimum as I usually am just topping up the charge when I’m at home with the correct charger.
As mentioned the li ion charger has a specific charging algorithm, you could turn your batteries into ticking time bombs (and not even know it) by using the wrong charger so its extremely unwise to attempt to use an incorrect charger.
In case you aren’t aware, reverse charging (If polarity is backwards) is known to often make li-ions get violent. Explode “rapidly disassemble” as they like to call it or vent with flame.
One of the nasty gasses that li-ions will release if they get violent is HF hydrogen fluoride. Upon contact with tissue, skin, eyes, lungs, it forms corrosive, penetrating hydrofluoric acid.
By the way, my 8.4V battery is on a 9V power supply charging as I type this. I just need a bit of power for emergency.
Definitely won’t recommend it as a main way of charging. Also I’m keeping an eye on it and monitoring temperature.
