Monday, April 18, 2016

[Random Teardowns] A couple of laptop batteries (aftermarket vs original)

Device: Original Lenovo 42T5225 (ThinkPad R61) and Chinese clone of 42T4788 (ThinkPad X100e)
Origin: Various
Reason for teardown: Broken
Impressions: I've recently opened up a few laptop batteries and decided to take some pictures. Keep reading if you've ever wondered just how different the Chinese aftermarket batteries are compared to the originals.

The original battery controller PCB is conformally coated while the clone is bare. Fair enough.

The original is based on the Mitsubishi/Renesas M37512 microcontroller (datasheet)

The clone on the other hand is based on the SINO WEALTH SH79F32 (datasheet)

Nothing terrible so far, right?

Well, if you take another look at the image with the original microcontroller there are two things worth mentioning on there. That component with the two long leads to the right of the micro is an externally triggerable fuse. It can blow during an overcurrent condition as any regular fuse OR the micro can trigger it in case of another hazard condition like say the cells overheating. Which brings us to the small flex cable temperature sensor stuck to the cell on the left side

Now let's see what the clone has in terms of overcurrent or overtemp protection.


Zero for two.

So the most the micro could do is (attempt) to shut the FETs off in case of an issue. (If it even noticed it before the cells set themselves ablaze.)

Lastly, let's take a look at the cells themselves.

The original has Japanese made Panasonic cells
The clone has Chinese made ChangJiang (CJ) cells
No surprises here. And it should be pointed out that these aren't necessarily bad or more hazardous than any of the high-end cells. If anything they're just unlikely to handle as many cycles before capacity loss renders them unusable. That said, a fuse and temperature monitoring still wouldn't hurt.