Test/Review of Kentli AA 2800mWh (Blue)

Batteries and Chargers Rechargeable Batteries
1

Kentli AA 2800mWh (Blue)



Official specifications:

  • Type: Li-polymer
  • Brand Name: KENTLI
  • Size: AA
  • Nominal Capacity: 2800mWh
  • Model Number: PH5/CHU4




This battery is not a NiMH battery, but a LiIon battery with electronic to make it look like a 1.5V AA battery. Due to this it will not be a normal battery review, I could not use my normal test scripts, but had to do a lot of the test manually. I have looked quickly at the charger and looked inside the battery.
The first thing I notice when I see the specifications is that capacity is specified in mWh not the usual mAh, this tells me that they try to make the battery look better than it is, as can be seen above the real capacity is about 1600mAh.




When I got the battery there was some trouble with shipping loose LiIon cells, this means I got the cells in a flashlight.



The top of the cell has a ring around the button top, this is used for charging the cell.








The cells has very stable voltage, until they are empty. This high voltage means they can be used in equipment that will not work with NiMH cells. The very stable voltage also means that any battery indicator will show full, until the battery is empty, there will be no indication of 25% left or anything like that.
The cells have a small difference in capacity.







I did try a low current discharge at 10mA, as can be see above the battery lasted a bit above 6 days and the capacity was around 1600mAh. This means that the extra loses due to the buck converter inside the battery is not really significant for a 6 day period.



I did not really hit the 2800mWh in my test, only 2500mWh.



The batteries requires a special charger or rather a LiIon charger, due to the voltage difference this charger do not need to charge 1600mAh, but only about half that.



Charger





To use the batteries you need the special charger for them or you can use a normal LiIon charger if you can make an adapter.



The trick is the connection to the battery, it must connect to the ring around the plus pole and not the button top on the battery.



The charger can only be used for Kentli batteries and can handle up to four at a time.



A fairly normal LiIon charge curve with 300mA charge current and 50mA termination.





The 4 channels do not completely matches in voltage, that might be the reason for the capacity differences in the batteries.



With 4 batteries the charger must be powered from a usb power that can deliver a bit above 1A.



Inside the battery



I had to see what’s inside this battery.



Some of the electronic is on a flex circuit board



The metal can is just a metal can, inside there is a lithium polymer pack and all connections are done with the flex circuit board.



This electronic handles two function. One function is the buck converter that reduces the LiIon voltage to 1.5 volt, the other function is shutting down when the battery is empty (To avoid over discharge).
The buck converter is the 2R2 inductor and the chip besides it, this chip is a 2.5A buck converter and does also contain a 2.45 volt under voltage lockout.
The other chip is in series with the battery and must also be some sort of protection IC, maybe to prevent overcurrent if the ring is shorted to the can.
Click on the above pictures for larger versions.

When I did have the battery open, I did some more measurements:

  • Standby current from LiIon cell: 30 to 40uA or 300uA
  • Cell capacity about 800mA (From charger charts).
  • Disable voltage about 2.4 volt.
  • Disabled current (When cell voltage is below 2.4 volt): 2uA
  • Minimum cell voltage to maintain 1.5 volt out (unloaded) is 3.6 volt





Conclusion

This battery is an interesting idea, what you get is:

  • Stable 1.5 volt output voltage until the battery is empty (This is close to lithium behavior).
  • Less capacity than alkaline, lithium or NiMH batteries.
  • A battery status readout will not work with this battery.
  • Less current capability than NiMH, but much better than alkaline
  • Unused cell will keep charge for 2 years (This is a guess based on standby current measurements).
  • Powering low current equipment it will discharge in less than 4 month (This is a guess based on standby current measurements).


With the above I believe the batteries are most useful when replacing lithium cells in equipment that uses them fairly fast, but batteries will have to be replaced/charged more often.
They are not good to replace alkaline in low power equipment that last a year or more on a single cell, due to the self discharge.
If equipment can run on NiMH, they are preferable compared to this cell, due to higher capacity and lower self discharge (for LSD cells).



Notes and links

How is the test done and how to read the charts
Compare to other AA/AAA batteries: Alkaline/NiMH/Lithium

2

ah

and here I thought it was a good battery idea

I guess nimh is still the best

3

very extraordinary battery.
I think this may not sell, ordinary people do not understand the benefits.
Even for experts, a very special charger is a problem.

4

Interesting battery type, however the need for a specialised charged makes it a costly product to adopt. Checking prices around for the charger and 4 batteries I’d rather stick to NIMH for now.

5

By the way, does this have the same hazards as lithium ions like unbalanced cells and reverse charging?

6

Very interesting battery. Reminds me of the “USB rechargeable AA battery”, same principle but better execution.

Which practical use could this have? I can only think of maybe a very voltage sensitive equipment that requires stable 1.5V to work properly, but then such equipment probably comes with an integrated DC regulator already.

I don’t think these are easy and cheap to produce, so why did they put so much effort into it, knowing that the performance is not much better than a cheap ni-mh. I’m intrigued!

7

A friend of mine used to have a camera that would only function properly on alkaline which got empty really fast, or energizer lithium.
With eneloops (even the 2500mAh) it would say battery empty in 10 minutes.
These batteries could be useful in such situations.
Other idea I had to test back then (but never got around to it) was nizn batteries. But those might have too high voltage and their self-discharge is higher.

8

Exactly, anything that has problems with NiMH. That kind of stuff is, of course, badly designed from the start, it will only use a little of the energy in alkaline batteries.

Another potential solution for this type of equipment may be the batteriser.com, but it is not ready yet.

9

Some cameras has a setup setting of battery type.
if battery type set as Alkaine than NiMH batteries at 1.2V considered as empty/low.
My cameras brand was Olympus and on NiMH setting it works OK.

10

Thanks for the test HKJ, interesting batteries!

I want some of these! They are perfect for a constant output flashlight (I'm a bit fixed on that ). Problem with the ones I made thusfar is that the 7135 chips that they use do not really put out a constant current, they are a tiny bit dependant on input voltage. I see a little project: 2xAA host, two of these batteries in series, a 1x7135 driver and a new Oslon Square.

edit: hmm, 38 dollar for two of these, project cancelled until next lottery prize coming through..

11

Don’t think the camera is still in possession to double check, but as far as I know it did not have a setting like that.
It was just a very picky camera. Probably wanted to force to use a special batterypack.

12

I’ve used the PowerGenix nizn in Canon (4xAA) flash units with good success. Cycles faster, no problems with excess voltage.
I also use them in nose hair trimmer and (cheap) single AA toothbrushes. Performance in both cases is clearly superior. You do got to watch them and not over discharge. They get ruined much easier than NiMh, meaning they simply are not suitable for the ‘average Joe’.