Charging rechargeable torch battery.

[Peter James]

I own a torch battery which has the following written on it.

"+ BRC 26650 3000mAH - L1 - ion 3.7V."

I want to charge it from a 13amp socket marked - "Total 5v DC 2.4a max (2 usb share) Surge protected".

Would I be safe in doing that with that set up?

PeteFJ

[Andy Burns]

Buy a USB to 26650 charger, many will charge varying length/width of LiIon batteries, you can from £3 upwards depends how much you trust it not to burst into flames!

[Animal]

You need a li-ion charger of course. 5v 2.4A would be enough to run a 5v one, though they're usually mains voltage. Don't try to circumvent good practice with li-ion, one violation is all it takes for them to go up in flames.

Li-ions are sometimes charged from 5v with just a diode to limit max voltage & resistor to limit current. It's not a great approach but is doable. You must of course ensure you use the right resistor, or it's hello flames again - and I'm not recommending it.

[Paul]

Batteries come in all sorts of configurations. Power versus energy, Lithium Iron Phosphate versus NMC maybe. Different cell voltages should mean using a different charger. It's not good for a charger to support two cell types, because "the user may make a mistake" while using it.

Here, we see experts review a potential purchase. Notice a small diagram which is a section of the actual datasheet for the cell. This tells us some of the necessary parameters. 4.200V top-up voltage, 0.1 amp current cutoff on top-up.

# And for amusement BatteryUniversity has all sort of info about charging.

"The advised charge rate of an Energy Cell is between 0.5C and 1C; the complete charge time is about 2–3 hours. Manufacturers of these cells recommend charging at 0.8C or less to prolong battery life;

however, most Power Cells can take a higher charge C-rate with little stress.

Charge efficiency is about 99 percent and the cell remains cool during charge."

You need this article to decode what "C" means. The test cell is 2300maH, charging it at 0.8C would be 1840mA charging current (first phase to 80% fill). Using

0.5C might be even better for the cell (by a small amount), increasing charge cycle time.

The precision charger (using 4.200V point), is part of the safety aspect for some of the battery chemistries. Lithium Iron Phosphate (used in fairy lights with solar power), can take more abuse above rated voltage, than your cell can. A precision charger likely works best (charge cycle count) for both cell types.

Paul