Normally my teardowns involve taking apart dead compatible replacement batteries, but this post is a little different. My latest netbook, an Asus eeePC R011CX seems to have developed a fault whereby the battery detection is intermittent. When charging from the mains, the battery sometimes shows up, and other times doesn’t. When running from the battery, it likes to shut down as soon as it’s moved.
I reasoned this points to a broken solder joint where the battery connector meets the motherboard or the connector on the battery itself. As the R011CX is a pain to take apart, and the unit’s useful lifetime is very limited, I decided against fixing it. It’s a 24/7 low-powered server at the moment, so the loss of the battery is hardly a show-stopper as it will run happily off the AC adapter alone. The battery did feel just fine though. Given it was produced in 2012, its time is pretty much up.
This left me with a battery that I had no use for. I couldn’t be bothered to try selling a second hand genuine battery, as it wouldn’t fetch me much money in return anyway. As a result, I decided to tear it apart so that we can see the difference in quality between properly engineered batteries, and the “cost sensitive” replacements.
Taking it Apart
Unlike the low cost replacement batteries, taking apart a genuine battery involves a higher level of difficulty. It took a lot of strategic prying with a flat-head screwdriver to get the case halves apart, which also involved copious amounts of damage to the case and a slight nick on my finger.
The top cover is now separated from the bottom, but the internals are still firmly stuck in place. On most compatibles, it only takes a slight nudge to convince the pack to “release” from the case, but in this case, it seems the cells are siliconed into the back. A bit more strategic prying finally released the whole assembly from the rear shell, although with a lot of damage to the rear.
In addition to a tight-fit design and silicone at the ends and at the rear corner causing damage to the green battery heat-shrink, there was also a line of double-sided adhesive running down one of the cells holding it into the rear.
The assembly itself uses high quality Panasonic CGR18650CG MH12210 2250mAh Made in Japan cells, resulting in a total capacity of 4500mAh which is a little more than the 4400mAh marked on the outside, probably because it takes into account a 50mAh tolerance in capacity of the cells – the markings on the outside are conservative, what a breath of fresh air!
The unit itself avoids wires, with only the ground of the pack being connected by relatively thick wire. The intermediate cell balance connections are made by solid tab connections, insulated by paper labels, and soldered directly to the PCB. This makes the construction very rigid.
As expected, there is a pack thermistor for safety and charge termination purposes. With some judicious use of sharp side-cutters, I finally liberated the main PCB from the battery pack.
The PCB is marked with SXP2361 2226A1C BLA4AE01 123A. The PCB has strategic “dabs” of potting compound placed over circuitry to protect it from environmental influences. This side contains the main pack controller. We can see the 0.005ohm sense resistor very close to the power connector.
The underside is marked with ETON ET866, date code Week 7 2012 with UR code E213441. More soft potting compound can be seen, with additional chips on the underside and a secondary protection current/thermal fuse which should kick in, should all else fail. This is considered an essential form of protection, omitted in most compatible batteries.
In what seems to be a space-saving and convenience related move, the fuse was mounted over a pair of TPC8117 P-channel MOSFETs. I suppose the fuse could possibly save the pack in case any MOSFETs burned through and an abnormal charge/discharge condition occurred.
Of course, there are a few more semiconductors scattered about, with vague markings. Anyway, lets look at pack construction, where we are in for a little surprise too.
Two different types of tabs between cells were used – one which folds vertically, and the other folding horizontally. Spot welds were extremely clean, and tabs were pretty much right for size.
There was also a spacing insulating “pad” between the cells, even though they are being connected at the same potential – I’m not sure but possibly the thin parts of the tabs could be acting as secondary fuses, or it’s a measure to avoid friction or corrosive cell vent products from eating away at the base of the next cell.
As expected for a pack that was not in trouble, all cells were very close in voltage.
The teardown of the genuine Asus laptop battery confirms what we all know – the original OEM batteries are built to higher standards than the compatible cells. The outside labelling is accurate when it comes to cell origin, and conservative when it comes to cell capacity. The physical build of the battery is very strong, and hard to disassemble, with everything fitting in snugly. The cells used inside are quality Japanese made Panasonic cells, with good quality pack construction, and a controller PCB that includes a secondary protection fuse which is often omitted in aftermarket compatible designs.