Performance analysis/review of Kentli PH5 Li-ion 1.5V AA battery

In my previous blog post, I tore down the Kentli PH5 battery – a Li-ion battery that has an internal 1.5-volt regulator that allows for terrific voltage stability… up to a point. In terms of data collection, so far I have collected 55+ runs of data logs (248 MB of text files!) and still do not quite have all the data I want. As for the data that I do have, I will be disseminating them with as much thoroughness as possible.

Voltage vs. load current

As expected, the voltage output of the PH5 remains quite stable, up until roughly 2.1 amps where the voltage sags noticeably until the regulator goes into overcurrent protection mode.

A maximum load capacity of 2.1 amps seems to be a bit… limiting. That said, I have not done tests on the PH5’s transient load capacity, as it would require more automated control than what I currently have available.

Another issue with having such a flat discharge curve is that any device that performs fuel gauging using voltage alone will report 100% capacity, until it suddenly shuts down. This could be a big problem for digital camera users, as they will have no indication that their batteries are running low, until the device abruptly stops working. If the camera was writing an image to its memory card when the battery died, it could cause the image to be corrupted, or worse, damage the file system on the card!

Voltage vs. state-of-charge

Unless you are running the battery at a high discharge rate, the output voltage will be flat at 1.5 volts before abruptly brickwalling and dropping to zero immediately at the end of discharge. At a high load (in the case of the graph below, at 2 amps), the voltage remains flat until the very end of the discharge cycle (99% depth of discharge for my test run), where it quickly tapers off and drops to zero.

Capacity vs. load

This is the big one, and it took a lot of work to get this data, especially at low loads (48+ hours of continuous logging is just asking for Murphy’s Law to come into play). I used almost 50 discharge runs to create the graph below.

This is where things get… interesting. I was expecting the capacity to peak at low currents then taper off as the load current increases. Instead, I noticed a definite ‘hump’ in capacity around the 250 mA mark (reaching a maximum of 1700 mAh / 2550 mWh), and only after that point did I see the expected downward slope in capacity, reaching 1200 mAh (1800 mWh) at the 2 amp mark.

This data brings forth some very interesting conclusions. The PH5’s capacity is inferior to its Ni-MH counterparts (even the relatively crappy ones), and at higher discharge rates it has similar capacity to that of an alkaline at the same load, albeit with much better voltage stability than the Ni-MH or alkaline chemistries.

Other findings

Although I won’t go into too much detail for the next few points (I haven’t gotten quite enough data to be presentable), there are some other issues with the battery that I think should still be mentioned.

One issue is the amount of heat the battery gives off at high loads. At 2.1 amps, I had to use a fan to blow cool air onto the DC-DC converter just to prevent it from entering its over-temperature shutdown mode. Although the converter itself can tolerate elevated temperatures, the Li-ion cell inside will not; the uneven heating that the cell will encounter could potentially degrade its lifespan in the long run.

Another problem is efficiency. At 1 amp, the DC-DC converter is about 75% efficient, and is only 65% efficient at 2 amps. I have not tested the converter’s efficiency at lower loads yet, but I doubt it will achieve more than 85-90% efficiency.

A potential issue with this battery is self-discharge. The buck converter remains active all the time, unless the converter or the Li-ion protection circuit enters a protective shutdown state. I have not had a chance to fully charge an unmodified battery in order to perform a long-term self-discharge test, but I will create another blog post for that, if/when the time comes.

Conclusion

Overall, I’m on the fence when it comes to this battery. Its innovative design does provide unparalleled voltage stability, but its low capacity even at moderate discharge rates dampens the fun significantly. Additionally, the 2.1 amp discharge limit could prove to be a bottleneck for some high-drain applications; this, coupled with the cell’s tendency to shut down abruptly when the internal cell runs empty could potentially cause file system corruption for digital cameras that have not been designed to handle such sudden power interruptions.

Also, the batteries are very costly. At about $10 per cell, you may want to think twice about replacing all your current disposable and rechargeable batteries with these newfangled Li-ion ones. Don’t forget the charger either, as a special charger is required to make contact with a recessed terminal on the top of the battery.

Overall, this cell is… interesting. Just don’t expect a miracle in a steel can.

Pros:

  • Excellent voltage stability, even at high loads
  • Li-ion chemistry allows for a very lightweight cell, even with the addition of a DC-DC converter
  • High output voltage could allow some devices to run more efficiently

Cons:

  • Low capacity – provides a mere 1200 mAh (1800 mWh) @ 2 amps, and up to 1700 mAh (2550 mWh) @ 250 mA (even alkaline batteries can do better than this)
  • Abrupt shutdown when the battery is overloaded, overheated, or over-discharged
  • Runs hot at high loads (and therefore is fairly inefficient)
  • 1.5 MHz converter and unshielded inductor can cause excessive EMI (electromagnetic interference) in sensitive devices
  • Expensive! Costs approximately $10/cell
  • Requires proprietary charger

Bottom Line: This is a niche product and should not be considered a universal replacement for alkaline or Ni-MH AA batteries.

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12 thoughts on “Performance analysis/review of Kentli PH5 Li-ion 1.5V AA battery

  1. Pingback: Teardown of Kentli PH5 1.5 V Li-Ion AA battery | Rip It Apart – Jason's electronics blog-thingy

  2. Super impressive review. Which rechargeable AA and AAA batteries you recommend to purchase ? What items can take only 1.2V or 1.25V rechargeable batteries ? .Some can only take a 1.5V battery. Guessing only flash lights and camera flashes can take the 1.2V rechargeables.

  3. Pingback: Self-discharge test of Kentli PH5 1.5V Li-ion AA (Part 1) | Rip It Apart – Jason's electronics blog-thingy

  4. Neat review. These are the curves that I wish that had come with the documentation.

    I use a pair of Bose QC15s pretty much only when I travel, so I’d prefer not to have to deal with replacing battiers. Unfortunately they don’t play well with NiMH rechargeable batteries because they drop out somewhere between 1.1V and 1.2V. Practically speaking, this means that they can only be used for about three hours whereas Alkaline batteries last closer to thirty hours.

    I’m hoping that the 1.5V output will let me operate my headphones for longer. The 20-30µA quiescent current is a little lame, but it’s not too hard to charge them overnight before a trip.

  5. I feel like you are forgetting the most important pros and cons.

    Pros compared to NiMH:
    No memory effect
    Little cycle loss

    Cons compared to NiMH:
    Calendar loss

    The amount of calendar loss would really be much more interesting to know than the self-discharge rate (as it’s probably much higher)

  6. Interesting review! These cells perhaps suit my need very well, that neither Alkaline nor NiMH rechargeable battery can do.

    I am using two techlite TE116 LED flashlight on my mountain bike. They offer promising illumination on extensive longitudinal and lateral range with 3xAAA. They require total voltage supply to be above a threshold at around 4V. Below that point, the luminance drops like crazy. Alkaline battery roughly sustain 3 to 4 hours use before dropping below 1.3V each, while NiMH ones would never work. 6xAAA alkaline battery are dropped out from my flashlight every two nights of biking. They still work on all kind of devices but not my flashlight.

    The LED of the flashlight should be rated less than 3Watt. Current draw should be well below 2Amp. I don’t mind charging the battery every night as long as they barely last two hours before starving. I can pack 3 more alkaline AAA for emergency.

    Let’s see if it works.

    • Some updates:

      Checked the specification of the LED of my flashlight, Cree XP-E 150 Lumen, current draw 1-1.5A, operable voltage around 2.8-3.4V. Turn out it wasn’t the problem of voltage drop, it is about current drop. GP ultra alkaline cells can provide ~1.4V and >1A supply for 2 to 3 hours, drop to ~1.2V 0.7A and fail to support the flashlight.

      Got a few eneloop pro AAA rated at 950mAh. They provide consistent supply at 1.2V 1.4A about 45mins before dropping dead. So… the ~600mAh Kentli cells are out of question. Their capacity is way way too low.

  7. Thanks! I’m interested to see that AA lithium is available at all as there were significant reasons why it was not possible to get these.
    1200mAh low drain is still better than the cheap “3000mAh!!!” junk being shipped with solar lights, verified capacity on these to be less than 700mAh and in some cases lower still.
    Might get some just to retrofit solar garden lights as this would be doable.

  8. Jason, thank you very much for this review, it is incredibly helpful!

    I am researching battery capacity for a personal electronics projects and your post as proven extremely valuable.

  9. I really can’t find the decent words to thank you as you deserve for this great test, it helps me to decide which batteries I should buy for my sound recorder, I was expecting buying these instead of Panasaonic eneloop pro. Really thank you

  10. Did I miss 2here you tested how long they hold a charge without use? Seems like the most important thing I want to know, but I don’t recall seeing it.

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