I have a bunch of unmarked 18650’s that I pulled out of some laptop batteries I had lying around. I plan to use these batteries to test several different designs/configurations, but I need to know the max current that I can draw from them. I have been searching all over, but I can’t seem to figure out how to test this.
Just to be clear, I am not trying to test the capacity, I am trying to test the max current that I can draw from them. For example, Samsung 25R’s have a capacity of 2500mAh, but the max current is 20A.
Does anyone know how I can test these batteries? Technical responses are welcome.
UPDATE: I found a bunch of old batteries at a thrift store in my town. They couldn’t sell them, so they let me have them for free! I have taken about half of them apart, and I have about 50 cells so far. I have a LUC V6 charger from Li-Ion Wholesale, and I used it to charge up all the cells individually. It has an “activation” feature that is supposed to bring cells back from the dead, and it’s working great! Most of the cells were around 2.9-3.0 volts, but a few were at 2.0 volts and under. The charger was able to bring back almost all of the cells. I have only found 3 completely bad cells so far.
Everything is reasonably holding a charge so far. I just started testing my cells with a 1157 style light bulb. This light bulb has two filaments, the smaller of which draws about 0.5 Amps at around 12 volts. I wired up my sleds so that I have 3 cells in series to get close to the voltage, and I have 2 of these sleds in parallel. This results in the load on each cell being about 0.25 Amps. I have two multi-meters set up; one to monitor voltage and one to monitor amperage. The amperage drops as the voltage drops. It starts at 0.52 Amps, and it ends at 0.45 Amps, but the difference negligible for my tests. I will attach pictures of my setup to this post.
So far, I have just been testing the capacity of these batteries. I wasn’t expecting much, but they are performing much better than I thought they would. I will be posting the results of my tests for each one.
Panasonic CGR18650A 2000mAh Max Current: Not yet tested Tested Capacity: 1083mAh I tested these cells at 0.5 Amps, and they lasted a little over 2 hours. I did not have two sleds in parallel when I tested these, so the amperage is twice as much as the rest of the tests. I will test again at 0.25 Amps when I get a chance. These cells are the oldest of the bunch, and they appeared to be the worst in terms of holding a charge. A day after I charged them, they dropped to about 3.95-4.00 volts and then stayed there.
Samsung 26D 2600mAh Max Current: 5.2A Tested capacity: test in progress I am testing these cells at 0.25 Amps. The are performing well so far. After charging, they stayed at around 4.13 volts. At full capacity, these cells should last this test for 10.4 hours. It has been 4.6 hours so far, and they are not even halfway depleted. They are currently at 3.735 volts.