Charging 18650s with unknown capacity?

Get a DMM. I strongly suspect that your wires are crap. Those can drop the voltage by a huge margin and might get warm at a 3A discharge. Or your cells are crap (although the fact that you still read a voltage of 3.021V after 10minutes backs my theory about your wires up). Only one way to find out -> DMM.

I just assumed that if you buy a hobby charger for 100 bucks you wouldnt go cheap on the cables..

Did I mention that you should get a DMM? Thats essential when handling LiIon batteries.

P.S.: Get a DMM.

Haha. Do you think I should get a multimeter or something? :P

I borrowed one and tested voltage as it discharged at 1amp.

There was a ~1.10v difference between what the DMM read and the charger read.

3.86v on the DMM vs 2.95v on the Charger.

While resting, the DMM read 4.01 and the charger read 4.053

My DMM readings were taken in the same place my alligator clips are attached to.

What should I do to determine if it's the cables that are bad or if I possibly have a bad connection/setup for the battery

Better question, how can I fix my cables? strip and resolder the clip and banana jack on?

What size wire are you using and how long are they?

The cables are the problem.

I just took one apart with the intent to strip and re attach.
The banana plug end has a "Binding post"? connection and there was no exposed wire.
I tried to strip an end and the wire just snaps, when you bend it, it breaks.

Since I already have the ends, what kind of wire should I get?
can I use one of the wires inside of an ethernet cable?

You can’t be serious about using wire from an Ethernet cable, that’s a data cable!
Go to your closest hardware store and get thick but felixible cable that can handle 10amps, this will be ideal low resistance cable for measurements or charging.


You could use a pair of them, though! They’re arranged that way and twisted for you. Maybe a couple of pair would be better. Maybe more, if you want to flow some decent current. Be sure to solder the ends together before wrapping them around that post! Cat6 Ethernet isn’t widely available as scrap yet, so you’re likely looking at Cat5. Either way, a dedicated, full-size wire would work better. If it has to move any, ever, use stranded wire, if it can be hot-glued into place, solid works fine.

If you have a computer repair shop nearby, ask for a dead Power Supply from their trash… Lots of wires there!

+1 on getting a DMM.

I was afraid I was being to subtle. :P

So the problem are indeed the wires.^^

While you are at the hardware store, pick up a DMM, so you dont always have to borrow one. You will need it a lot.

I built alligator wires with thick speaker wire, works great. Something between AWG16 and AWG14 should do fine. All assuming you have a soldering station. ;)

In your other thread someone posted a picture of a "clamp". Those are far better than attaching the wires with magnets.

Someone gave me some broken multimeter leads and I used those wires and soldered on the ends.

Discharge actually worked and I have a battery that's has been charging for 4,000seconds at 4.2v.

I bought 10 pair of red+black leads and not 1 of them gave the correct voltage... Going to see what the seller has to say about that.

For an 18650, do I discharge to 3.0v or 2.8v for a capacity test?

I would recommend 14 AWG high strand count silicone wire, very flexible stuff and is usually what hobby charges are supplied with. You can find it on ebay if you prefer that route. DMM leads are usually silicone wire also, but are usually around 18AWG wire. The larger and the shorter the wire you use the less v-drop you will see especially at higher currents.

Depends on the battery, the newer Panasonics can be discharged down to 2.5v. Member HKJ usually discharges down to 2.8v for his graphs. The datasheet of a particular battery usually contains the current draw and the ending discharge voltage of their test, to check the advertised capacity. Most of us test at what actual current draw we will be using the battery at, to determine the runtime or capacity in actual use.

Those are usually way too thin. Get some thick speaker cable.

4.000 seconds at 4.2V? Thats over an hour. Too much imo.

Correct voltage compared to what and in what state? If you bought thin leads, thats no wonder.

Depends. 4.3/4.35V cells -> 3V. Most cells -> 2.75V. Panasonic NCR and some IMR cells -> 2.5V.