The hazard of after market batteries

I usually start my work day with video calls. My office is in a co-working space, I have my own desk in an open space, and I use a desktop computer there. I tried to use my phone and desktop for video calls, but after a few months I wanted a laptop to be more comfortable. I needed the laptop to be able to speak privately in meeting rooms or phone booths, and work while away from the office or home.


I love Thinkpads, and I’m cheap; paying $1,000+ for a decent modern laptop is out of the question. I go vintage and buy used gear.

I wanted to use a CS13 dock, I have fond memories of using one with a Thinkpad T440 back in 2013. My decision was driven by nostalgia, it was a cheaper way to get over my midlife crisis than buying a vintage car or a box of high-end Cuban cigars. The puny USB-C whimperbolt ports in use today are inferior to the mighty CS13 docks. With the CS13 you slap the laptop on top of it and clack it’s docked; the laptop is connected and secured, ready to take off and do some work. The Thinkpad pushes into the board of the dock, inserting the port in, and two hooks get out of the dock’s board to grab onto the chassis to secure it. The clack sound is the port getting in the laptop and the hooks grabbing onto the chassis, it all happens at the bottom of the computer, it’s safe and efficient. To undock there’s a big fat button on the side, push it and the laptop pops out.

The exquisite Thinkpad Pro Dock

To easily carry the laptop around I wanted a small form factor, so I went for the X series sporting 12" screens.

The Thinkpad X270 is the most recent choice for the CS13

The CS13 port was discontinued by Lenovo with the introduction of an inferior docking solution based on USB-C, this new solution require an additional step to connect the port on the side compared to the old docking solutions. In my opinion it is a step backward, new isn’t always better.

We have to look for models released before 2018 to get CS13 support, the winner is the Thinkpad X270 released in 2017. Since I was shopping for a 5 years old model, I wanted to max out its configuration. I looked on eBay for a week and took a risk by buying from a relatively new seller since their offer looked great on paper, it was advertised a “almost new” with the following configuration:

The X270 usually runs with 6th generation Intel processors, luckily the one I got had a 7th generation, probably because it was produced later. It cost $335 plus shipping, and arrived a couple of weeks later. The laptop was in pristine condition, the keyboard barely had any wear, the only imperfection I found was one tiny dent on the side, otherwise it was spotless.

My precious
My precious

The batteries’ life time

The X270 has two batteries: one internal and one external. The external battery gets drained first, and when it’s empty the computer switches to the internal one. The external battery is hot swappable, I can slide it off while the laptop is running and plug in another fully charged battery.

The external 24 kW battery reported it had only 70% of available capacity. The battery was usable but close to the end of its life, it wasn’t surprising since the laptop was 5 years old. I got around 40 minutes of video call from the external battery alone, and got 60 more minutes with the internal battery which didn’t age as much and still had 89% of its capacity left.

I needed a fresh external battery to get the life time I wanted.

Looking for an upgrade

There are three types of external battery compatible with my model: the 3 cells 24 kW that shipped with my X270, the 6 cells 48 kW, and the 6 cells 72 kW. I wanted to get a 6 cells to make sure I could get 2 hours of video call time. I looked online, and found a 72 kW after market battery compatible with the X270 for $60 on Amazon.

I ordered it, as soon as I got it I popped it into the Thinkpad and fully charged it. I joined a lightweight video call with the laptop and it had more than 3 hours of estimated life time with the external battery alone. With this new power source I more than tripled the autonomy of my Thinkpad! The downside was that the battery stuck out of the body of the laptop, making it a bit chunkier. I was happy with the trade off.

There’s something with the battery

The next morning I arrived at the office and got ready for my morning calls using the X270 decked with the new extra large power-bank. At the beginning everything was good, but after 10 minutes the video suddenly started lagging and the sound got choppy to the point of being unintelligible. Why was the sound and video suddenly so slow? I immediately opened a terminal, checked the network and it looked fine. The laptop felt sluggish, I opened the resource monitor and saw the processor was 100% busy. Curiously the fan was not running, and the processor’s temperature was below 40 degree Celsius... What the hell was happening? It turned out the processor’s frequency was stuck at 400 Mhz, way below its normal boost speed of 2.8 Ghz.

I got the charger, plugged it into the laptop, the problem was instantly gone, the processor scaled up its frequency, and everything was back to normal in the video call. I finished my morning work with the laptop plugged in, and started looking for a solution to this problem online. I found this Reddit thread where someone described exactly the same problem I had: the CPU was throttled at 400 Mhz with a third party battery.

Not compatible with laptop’s EC

There’s a circuit in the Thinkpad that protects it from drawing too much or too little power from the battery, if it detects that the battery power delivery is outside the bounds of what it considers acceptable this circuit forces the processor’s frequency down to 400 Mhz. It is calibrated with the characteristics of genuine batteries, unfortunately the aftermarket one I received didn’t quite meet the specification of the original Lenovo batteries.

The internal battery and the old external battery don’t exhibit this processor throttling problem when they power the computer.

Aftermarket batteries aren’t a sure thing

Beware of third party batteries, compatibility isn’t guaranteed even if it’s advertised. I am glad it was easy to return the one I ordered, and from now on I’ll make sure that third party batteries have a good return policy to avoid getting burned. I am now getting a used genuine Lenovo 48kW battery from eBay, at least I know this one will work, and I’ll get a good 2 to 3 hours of video calls with it.

Previously: I installed a new battery on my Thinkpad X1 Carbon