Idiots guide to testing batteries ?

Hi all

I’m after an idiots guide to basic battery testing

How can I test if the Mah rating as specified?
How can I tell if a cell is knackered ?

How should I test individual cells ?
How should I test sealed packs ?

What equipment do I need ?

I have a basic multimeter and a WP6 charger

Sorry I should say I’m referring to Lion 18650’s

You can’t.
Voltage alone is of limited use and your charger provides no capacity data.

You need something that can do a charge with mA capacity input data and a similar discharge. I’d say minimally you need a hobby style charger like the Accucel-6 (I’d avoid the cheap eBay IMAX B6 as there is a flood of ‘fakes’ with potential problems on the market).
If you think you need to discharge over 1A you need to upgrade to a more powerful charger or get a specific discharger that can do the required level of discharge.

Some better (more expensive) chargers can do internal resistance reading which is quite useful.
Individual cells are easiest to test. Packs are MUCH more difficult unless there is a balance tap, which is not common on Lion packs.….0…

A rough estimate to get amp/hour of a battery using only a MM.
Measure the tailcurrent of your lights, find one close to an easy number to work with, 1, 1.5, 2A etc.
Fully charge the battery, give it 10 min to settle then put it in the selected light, note the time and turn it on.
If the light and battery has no low voltage cut off watch for the light dimmimg to an acceptable level, much easier to use a light with low voltage cutoff, when it goes out you know how long it lasts.
You now have enough info to work out the amp-hour of the battery.
If it was drawing 2A and lasted for 1hr 15min then it is 2*1.25 = 2.5, so 2400 or 2600
If 1.25 for 2hr 10min say 12min (easier to work with), 1.25*2.2 = 2.75 so 2800 or 2600

As I said it is rough and ready, but hey when its all you have, you have to go with it :bigsmile:

Cheers David

Thanks for that Pomme, I have found a lamp with a big heat sink that draws 2A so I will do what you have suggested.

I’m also thinking of getting a SO Shine SC-S7 which has a Mah indicator so I should be able to identify the best cells and see which are fakes

Can anyone recommend a fan for testing ? Is a big 30inch tower fan or a small PC fan best ?

I use my Trustfire X9 to test cells. On the Acer Aspire Samsung 2600’s it lasts almost exactly 62 minutes on high before the low-voltage warning kicks in (down to 3.15v resting). Driver is a 3040mA 105C, starts out around 2.8/2.9A and finishes at 1.9A. Treat the voltage drop curve as a linear drop and that nets an average draw of 2.4A, meaning that the Samsung purple-pack-pull cells are about 2400mAh and change from 4.15v down to 3.15v. That’s about in line with what HJK tested these cells being. (though he can do 4.2v down to 2.8v.)

The convention on end of life seems to be when they are below 80% of their rated capacity. If dealing with decent cells, that'll be what's written on the wrapper x0.8. If it's no name or ludicrous capacity cells then down to 80% of whatever they did when you got them.

That said, I had some "900mAh" 14500s that were down to 20mAh when I checked them.

Yes, I’m trying to figure out how to tell the factory fresh ones from the near end-of-life relabeled ones pulled from a hard-used laptop etc before I buy them …

That probably only applies to 18650s. AFAIK no laptop uses 14500s. But I've been wrong before.

Yep, 18650’s … how can you tell if they’re new vs. rewrapped pulls and possibly near end-of-life. Links to reputable distributors / sellers anyone?
Thx :]

(sorry ’bout the thread-jack)

How to tell before you buy? Only buy from well trusted sellers. Its the only way.

Never buy trustfire / _any_fire, they are often counterfeit rewrapped old cells.

RMM is a great trustworthy source. Panasonic NCR18650B Protected 3400mAh There is currently no better price available for quality protection. Seiko IC and 3 x AO8814 MOSFETs.

Banggood, wallbuys and other direct chinese sellers sell “protected” batteries. Junk protection added by a mystery company & clear wrapped over the original wrapper (panasonic, sanyo, etc). Too many reports of them failing, worse then straight up unprotected imo.

-Just what I was looking for — Thanks !!!

I think I got their last last 2 : Panasonic NCR18650B-PROT

I think the easiest thing to do is buy a hobby charger like a Thunder AC680 and just do a discharge test. They aren’t as accurate as an Electronic Load or a CBA IV, but they are accurate enough. Almost all of the hobby chargers use the Turnigy Accucell 6 controller, so you will have to use the NiMH profile to discharge down to the standard 2.8v, as the LiPO profile will only go down to 3.0v. The industry standard discharge current for testing battery capacity is .2C, which is the battery capacity in amps multiplied by .2. So in the case of a Panasonic NCR18650B, which is 3400 mAh, .2C would be 3.4x.2= .68A, so you would set the discharge current on the hobby charger to .7A.

I recommend the AC680 because it has a built in AC power supply and does not require a separate power supply. If you want something that is more accurate, you can go with a iCharger 206B, but for your purposes, I think it is overkill.

They come with a USB adapter so you can run a discharge test on your computer. They look like this when they are done. They tell you the voltage, discharge current, and total mAh.

Here is a test I did with a Redilast 3400 mAh NCR18650B down to 2.8v:

You can see it discharged 3144 mAh.

One big warning on Panasonic 3400 mAh protected — it may be too long for your light.

Or too fat.

Thrunite TN30 I'm looking at you....

Don’t you really love when a light has trouble fitting protected?
There is no reason at all. Bore the tube a half a mm wider. To accommodate the couple mm difference in length, they have these cool things called springs.

I have no issues with my cheap, maybe fake B6, but I don’t use it unattended, charging and testing only when I will be working at my desk nearby. It automates a reasonable testing process, which include several charge and discharge cycles. Once you have a fixture to hold half a dozen batteries at a time it is about as good as it gets for testing.

First protected cells I bought that was immediate issue, does not fit.

IMHO protected cells are a stopgap measure, protection needs to be in the driver, not the battery.