Klarus EP10 18EP-20 18650 Battery Issues

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Klarus EP10 18EP-20 18650 Battery Issues

I picked up a Klarus EP10 on Amazon, at a price too good to pass up, sold by Klarus Direct and no other indication it is counterfeit.

Included battery seems faulty.

Should’ve read the reviews first, have same issue as multiple reviewers, light only works for a moment with fully charged (by its own USB charging circuit) battery then slowly blinks, won’t change modes nor display battery capacity. However unlike a couple other reviewers, swapping in a different 18650 resolves it on mine.

Out of the light the protected, supposedly IMR 2000mAh “18EP-20” Klarus branded cell measures 4.04V. My replacement battery keeps it running without blinking, now drained to 3.6V and still going.

Now the odd part. I put the Klarus battery in a different light, and that light seems to work fine with it. Put the Klarus battery back in the EP10 and now it seems to work fine with it too. The battery had not been recharged since it last exhibited blinking mode only.

This suggests to me that the problem might be a bad contact between the protection board and the battery and that putting it in a different flashlight subjected it to more spring tension which (temporarily?) helps.

I attempted to measure current with a multimeter but with the Klarus battery, which now keeps the light steady on in high mode, starts to blink again with the multimeter in series. Substitute battery does not do this, can stay on but is only drawing ~850mA @ 3.6V.

Unfortunately I did not measure internal resistance when the Klarus battery was making the light blink, but using a charger, now it measures 100mOhm, older replacement cell measures 22mOhm. I know not accurate but the relative difference between aged replacement and new Klarus cell seems a lot for an IMR 18650.

Random info: Using the unprotected replacement 18650, at about 2.95V it drops out of (and won’t go back into) high mode into a lower than normal medium mode, maybe 150lm but still not blinking, then at about 2.85V, drops down to low mode and still not blinking, then blinks much dimmer than with the Klarus cell, at about 2.83V.

Edit: Managed to make the blinking problem reappear with the Klarus cell by shaking the light. I mean it keeps blinking after I stop shaking it. Shaking light with substitute cell does not make it blink.

Edited by: Dave_C on 03/25/2021 - 19:20