How risky is this?

I received a light for review, it takes two 18650, i have some that have a couple dozen cycles on them (not balanced) and are unprotected, and the light uses them in parallel connected by springs and metal in the battery carrier (like you would see 3AA connected in series in a carrier these are side by side in parallel)
I am not planning on draining the batteries, just testing tailcap current, hotspot and maybe 10 mins of use to see how much the light heats up.

i would limit use - maybe ok to test for a few minutes but dont plan on doing any runtime or heatsinking tests

Being in parallel, it does not sound like a problem at all. They will somewhat balance themselves.

If the cells are parallel, you have nothing to worry about. Use two cells with equal charge and they will stay exactly the same as they discharge.

as they mentioned above, in Parallel they will stay balanced in voltage with each other. Just make sure they both are fully charged in a good charger ( like an i4) and check the voltage after they been resting out of the charger for 30 minutes or more, to make sure the open-volts are within a 0.01 of each other.

The potential problem comes from using cells with significantly different properties. If the chemistries or health do not match you can end up with one cell carrying most of the workload. If you are reasonably confident that your cells have roughly the same type, age, batch, etc then I think the other posts here have you covered.

They are the same batch cells, from the same order, sanyo ur18650fm, both were used maybe 30 charges in one cell lights, they have only been fully discharged twice each, and are currently being charged on a ML 102 charger which charges to 4.11V

In that case it’s as I said above. I agree with the others who say not to worry. The cells will remain in balance, it’s hard not to when they are in parallel.

They have no choice :slight_smile:

Lets hope they don’t go on strike or form a union, or i will have to go nuclear

No no, if you anger them, its the Li-ions that get to go nuclear. You get to run.


their contract forbids them from going nuclear, however that feeds into my other thread on the same light

In this situation it sounds perfectly fine. The only time you will get a problem is in high drain setups. Sucking the guts out of the cells will amplify the different internal resistance and they will have trouble staying balanced.

Contact? :smiley: With li-ions? Poke ’em and see what that contract is really worth.

they insisted on explosion rights but i used my veto power to forbid nuclear type energy release