Teardown of Kentli PH5 1.5 V Li-Ion AA battery

June 17, 2015 – Performance analysis/review HERE!

After having an entire month of dormancy on this blog, I’m finally beginning to cross off the blog posts on my “Pending” list.

Last year, I made a blog post talking about Kentli’s lithium-ion based AA battery that has an internal 1.5 volt regulator. The first order never arrived, and the second one had arrived a few months ago but I never got to actually taking one of the cells apart. That changes today.

Cell overview

The battery itself looks like a regular AA battery, except for the top positive terminal. There’s the familiar ‘nub’ that constitutes the 1.5 volt output, but also has a recessed ring around it that provides a direct connection to the Li-ion cell’s positive connection for charging.

 

After peeling the label, we are met with a plain steel case, save for the end cap that appears to be laser spot-welded. Wanting to take apart the cell with minimal risk of shorting something out inside, I used a small pipe cutter to gently break apart the welded seam. Two revolutions and a satisfying pop sound later, the battery’s guts are revealed.

Battery internals

The PCB that holds the 1.5 volt regulator is inside the end cap, with the rest made up of the Li-ion cell itself. Curiously enough, the cell inside is labeled “PE13430 14F16 2.66wh” which is interesting in more than one way. First of all, the rated energy content of the cell is less than what’s on the outside label (2.66 watt-hours versus 2.8), and the cell inside is actually a Li-ion polymer (sometimes called a “Li-Po” cell) type; I was expecting a standard cylindrical cell inside. Unfortunately, my Google-fu was unable to pull up any data on the cell. I might attempt to do a chemistry identification cycle on the cell and see if TI’s battery database can bring something up.

Battery circuitry

The end cap’s PCB uses a Xysemi XM5232 2.5 A, 1.5 MHz synchronous buck converter to provide the 1.5 volt output. According to the datasheet, it is a fully integrated converter with all the power semiconductor components residing on the chip itself. The converter is rated for 2.5-5.5 volt operation, well within the range of a Li-ion cell. Additionally, it has a rated Iq (quiescent/no-load current) of only 20 microamps. The buck converter’s 2.2 microhenry inductor is magnetically unshielded which may cause some increased EMI (electromagnetic interference) emissions, but I don’t have the equipment to test this.

I was looking around for the battery’s protection circuit, and found it on the flex PCB that surrounds the Li-ion cell. It uses a Xysemi XB6366A protection circuit which, like the buck converter, is a fully-integrated device; there are no external protection MOSFETs for disconnecting the cell from the rest of the circuit.

Performance analysis

December 14, 2015 – After extensive and detailed analysis (148 MB of text files!), I’ve analyzed the battery’s voltage and output capacity, which can be viewed HERE (lots of pretty graphs; check it out!).

The data doesn’t stop there. Over a long, long period of time I’m tracking the battery’s self-discharge as well. Those posts are available here (Part 1), here (Part 2), here (Part 3), and here (Part 4).

Ramble: 1.5-volt lithium polymer AA battery? What sorcery is this?

Been a while since I’ve posted anything on here, but I decided to share my thoughts on a peculiar AA battery.

This AA battery is the Kentli lithium-polymer AA cell. It has a built-in 1.5 volt regulator that converts the typical 3.7 volts down to 1.5 volts (open-circuit at least). I bought a 4-pack of these cells from AliExpress back in October, but have yet to receive them. Even though I haven’t gotten them, there is some things that I’ve taken note of.

Current/voltage output

A graph promoting the battery discharge curve of the Kentli cell is shown below, taken from a sales page on AliExpress (rehosted on this blog to prevent image bandwidth-hogging):

705255222_102The interesting thing I found out was the green dashed line. This is supposed to represent the output voltage when used in a wireless microphone. However, the graph itself provides no meaningful data because no current loads are specified at all. In an attempt to get some sort of information from the graph, a Google search for a spec sheet for a typical microphone gives a discharge current of 125 mA. But a 0.3 volt drop at 125 mA? I dunno, this doesn’t seem right.

Safety

From a safety point of view, I’m not sure about how much temperature would rise in the cell from high current draw and whether overheating could occur in use, and if any typical Li-Ion protection circuitry is used (voltage and discharge protection). Given how this is made by some relatively unknown Chinese company, who knows.

I’m not saying anything definite until I see these cells and have a chance to get my paws on them for testing and disassembly. Until then, we’ll just have to wait.