iMax B6 Mini: 18650 Li-Ion charging


I bought an iMax B6 Mini charger, however it’s acting weird. I am trying to charge my older 18650 batteries (from an old laptop).

Result (double checked):

  • charge @0.5A: 1162mAh
  • discharge @0.5A: 1444mAh

I charged/discharged twice and the result is the same.

How is it possible that discharge rate is always higher?

Second thing that I compared this charger with a simple TP4056 charger module and checked result with an USB charger doctor device + discharged in a ZB206+ battery tester. The result was closer to 1400-1500mAh.

My question is: why iMax B6 mini can’t fully charge my battery or why it’s finishing charging too early?

Bonus: I get cca. same results with my NiMh batteries.

Just wondering, was there a ‘resting’ time period, when you were doing the Charge and Discharge tests?

(or did you immediately Charge after Discharging to cut-off voltage, and also immediately Discharge after they were fully charged to termination voltage?)


I’ve noticed with older (‘bad’) cells, the Charging capacity will generally be more than the Discharging capacity (ie. it takes more energy to get them up to “Fully charged” but the energy it can give out is less).

However, I’ve notice a “bad” cell that when rested for some time, its voltage goes up by itself a lot, so it seems to take less energy to charge them up to the termination voltage. I’m not familiar with the IMax B6 mini charger though…

The first aspect I would like to mention is that many, many iMax products on the market (regardless of distribution channel) are not authentic. Not saying you did anything wrong or picked the wrong product; but sometimes even the best merchants get stock from an unknown source. An iMax that isn’t authentic has all sorts of issues with termination voltage and/or the software (some can be flashed with new firmware).

Assuming your product is authentic (authentic ones cost approx. 2-3x more than the clones):
Due to RC and FPV hobbies, I have tried quite a few different hobby chargers. The discharge capacity and the charge capacity frequently don’t match up. There are various reasons I noticed, also, based on various forums (rcgroups, fpvlab, …) this behavior might be explained with this:

- when discharging a cell the voltage drops to a lower value than the cell would have without a load (this is normal) - the charging algorithm needs to be “set” or adjusted to the right discharge termination voltage to reflect a more accurate capacity. The challenge with some hobby chargers: the user has to find the right spot as measured voltage and actual voltage are not the same. Also, I have seen different behavior on different cell brands and models.

  • this behavior also happens the other way - when charging, the cell voltage might not be the same as the measured voltage and charging terminates prematurely (typically, the voltage measured by the charger was too high in my case).

Pretty much all cells I own show different capacities when charged/discharged across different hobby chargers.

I know this won’t be a solution for you ultimately, but try playing with the settings and voltages on your iMax.

edit: Forgot: Welcome to BLF!

I’m also familiar with the iMAX authenticity problem. If you got it ‘on the cheap’ it may not be a real one. They can have an assortment of bizarre problems, often only showing up if someone with some knowledge is paying attention to it’s behavior.

If you have known good cells I’d try the experiment with those. If you get similar results it would start to point the finger at the charger as the problem.

You absolutely will get different results analyzing cells with different chargers. As much as possible you have to make sure charge/discharge settings are identical. The worse the cells for this, the more out of line the results get. Old NiMh can be quite variable.
Even so, if you end up within a few percent you are doing fine.

(side question: the genuine iMax B6 Mini is from SkyRC right?)

Maybe charging is with higher voltage than discharging. E.g. 2A * 5V = 10W, but 2A * 4V = 8W.

Yes, but the clones literally look the same or very similar.
Hobbyking afaik has the real deal.

It can be VERY hard to tell the counterfeits apart.