How do you find the Mah of a rechargeable battery?

Okay guys, I’m an expert in some areas……this isn’t one of them :smiley:

I picked up a multimeter from HF because well, it was free with my purchase. So I learned how to find the voltage on a battery. Found out that one of my 14500 is bad. What I’d like to know is how you can find the mah of a given battery. I see folks here testing various batteries and I’ve learned a lot about the cheap Ebay batteries from them. Can I do this myself? If so, how? Will this free little multimeter do the job or is there a different piece of equipment I would need?

I know this is second nature to a lot of you, so bear with me as it is a new area of interest. Thank you.

I don’t think there is any way to determine a bettery’s capacity (mAh) with a multimeter. You would need a hobby charger or something similar. I would recommend this one, it is inexpensive (relatively) and works well:

You need a 1 Ampère load and a clock.
If it takes 1 hour from 4.2 to 3.0 Volts, it’s 1 Ah (1000mAh)
Don’t forget to make decimals of the minutes!
A 3x 7135 driver is 1050mA, to put you in the ball park.
Otherwise it’s just current x time
For a single 7135 it’s 350mA (or 380, check it).
Jut multiply with the time it takes.
It will have more capacity with a smaller load (due to internal resistance of the batt)

The Soshine SC-S7 is a handy little charger that will give you a fairly accurate capacity measurement of both NiMH & Li-Ion cells, especially if fully charged from empty but ideally a hobby charger is the way to go i think.

HKJ Review Soshine SC-S7

Or the Opus BT-C3100

If you don’t have a known load and you don’t have a clock you could also buy a charger that measures it.
It will probably multiply the time with the charging current.

I would also suggest the Accucell 6 link to us warehouse My one also does internal resistance

A review reviw link

In my view a hobby charger is the way to go, I will hold off judgment of the new analysing chargers for a while yet, some of them are a bit too new.

O wait…
The current will drop with a flashlight (driver and LED) when it reaches Vf of the LED, which is usually higher than 3 Volts….
You could try red LEDs, they have a Vf of 1.9 Volts…

…never mind then…

The easiest way is to get a charger that has capacity measurements built in.

The hardcore way is to discharge the battery through a resistor and measure the output in A over time. Plot the Amps against time, the area (Capacity = Current * Time) gives you the capacity. Actually you perform an integration, adding up the capacities recorded for each slice of time. There are some advanced multimeters that automatically measure the current with a specified interval, and sends the measurements to a computer. Then you can use the computer to calculate the capacity.

If you do the lights and resistor thing you’ll get bored, walk away, and end up with a dead battery, as in very dead. :stuck_out_tongue: Been there.
Plus you can use the charger for all kinds of things, test NiXX, LiFe, PB…… Just the other day I topped off my car battery. :slight_smile:

AVOID IMAX B6 unless you KNOW for certain it is not a fake. Cheap+eBay=fake=problems.
You WILL need a power supply. This type of charger ALL run on DC. The ones that ‘claim’ to be AC/DC simply have a cheap 5A power supply in the upper half. Better to get a separate PS. The embedded ones don’t vent heat as well and are more likely to fry.

Even the genuine ones are all not peaches, They still don’t seem to have learned and speced better resistors. I have a genuine one and am going to have to replicate the kit that was doing the rounds and replace a fair few resistors.


Put up the post then went out to the garage to start some chores. Came in for a protein shake and thought I’d check the board and I now have a wealth of information and several links. Big thanks! Very much appreciate the education.


When did you get it? That was a BIG problem a few years back. Then I thought they cleaned up their act. Then the fakes started showing up about a year ago. People go for cheap and newbies don’t have a clue so they still sell a lot of the junk. Pity. There are much better ones for a few $$ more.

The smart guy will measure the voltage and calculate the ampere, its more precise. But you need to do a reading each few minutes for a couple of hours.

A multimeter with a computer connection and some logging software will make it much easier.

This way is best to use only with protected batteries. Do remember that the discharge current will vary with voltage, i.e. you cannot do curves like me at specific current, but have to say discharge at x ohm.

Got it early this year, blew up an Accucel 6 trying to mod it to work with 4.35 cells. H’king of course did not have any, so went with the genuine B6. I also thought they had cleaned up their act but my one is only just acceptable and almost at the limit of calibration.

I do agree with your point about paying a bit more, The B6 in comparison with my iCharger is, well no comparison I’m afraid. But it is a fair bit more costly. And even I could not justify pairing iChargers rather than going for a cheaper alternative that would do the job.

The Accucel 6 was good for it’s price and better than my B6 for balance consistency. So nowadays I think that it is the best entry level hobby charger.

That’s interesting. Guys (newbies mostly) are buying them a lot because of price. All of those 4-button chargers look pretty much the same. What could possibly be different?
Folks are having a lot of problems with them with accuracy or charging other chemistry. I did think the authentic ones were OK.
I have the AC-6 and outside of the squeaky fan (needs lube occasionally) it’s a good unit.
I use mine to check battery capacity frequently as well as normal charging duties.