When you have the same smartphone for almost 3 years, it’s likely that your original battery’s not going to last as long as the service contract. And as long as you’re not an iPhone user you will probably look into a replacement or spare battery.
My first replacement cell was a 2-pack of “1800 mAh” batteries for $5. These had 66% of the stated capacity and TI’s Impedance Track gauge said that the DC internal resistance was about 250 milliOhms. That’s… pretty terrible. Those two cells quickly led their end in a battery recycling bin. My next two were “genuine” cells from eBay. They cost about $12 each and had rather authentic-looking labels on them too. Their performance was pretty good, but one of them became all bloated so I decided I’d take a look at the cell that’s inside. I peeled off the label, and the truth comes out…
This battery was an outright lie in terms of capacity! 1350 mAh is about 80% of the 1650 mAh capacity that was written on the outer label. The cell’s manufacturer is unknown, but the battery markings read “BMW-524655AR 1350mAh 2012.09.03.1110”. Wait, look at that manufacturer date. Something’s fishy…
The outer label states a manufacture date of July 20, 2012. The internal cell states one of September 3, 2012. Unless this battery was manufactured in a time-bending factory, then these batteries certainly aren’t genuine.
Next up was the protection circuit. The “genuine fake” battery uses a DW01 protection IC and uses a generic 8205A dual NFET for swiching. And there wasn’t even a thermistor; the PCB uses a 1.5k ohm resistor to simulate one. A genuine board uses a single SMD package that integrates the FETs and the protection IC.
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- “Genuine fake” protection board
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- (piece of) Genuine protection board. Note how there is only one SMD package.
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- Contact differences. Top = genuine, bottom = fake. The fake has fatter contacts for the two outer contacts.
Below is a comparison of the protection board of a fake battery and a “genuine fake” one. At least the “genuine fake” uses the same black appearance of the original.
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- Both of them mention that it’s a Samsung Galaxy S II replacement board. At least the fake one had the courtesy of labeling the pinouts…
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- Comparison of the two DW01-based protection circuits. Almost identical.
The “genuine fake” battery, after only 2 months of usage (not even 20 charge cycles’ worth), became so swollen that I can’t keep the back cover on. Running this battery through a bq27425-G2A battery gas gauge determined that the real capacity of the battery is a paltry 944 mAh, with an average internal resistance of 187 milliOhms. Absolutely pathetic.
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- Test rig using a bq27425 gas gauge and a 15-ohm power resistor. TI’s Impedance Track algorithm calculates the cell’s capacity and internal resistance.
Goes to show you get what you pay for. But some things may be more deceiving than others…
Rip It Apart - Jason's electronics blog-thingy 