Testing laptop battery: pinout, SMBus, charge capacity

As a result of visiting Hamfest, I ended up with a laptop to take apart – a fairly new Toshiba Satellite C675D with a broken screen. It’s not a Hamfest if you don’t bring home something to take apart of course! Today we’ll be testing the battery it came with to see if it’s salvageable.The date code says  it was made in 11/2011

Initial measurements

Label data indicates we are dealing with a 10.8V 4.4Ah pack. Since a typical Li-Ion cell is around 2-3Ah and 3.6-4.2V, that tells us the pack has 6 cells arranged as 3Series2Parallel (or 3S2P). The battery was fully depleted at the time of purchase and would not power the laptop. I could also not see any voltage present on any of its pins. Since we are dealing with a parts laptop here, an easy way to figure out full pinout is to look at the motherboard end of things:
It is pretty obvious that the larger blades are power and ground, and by measuring resistance to case ground we can tell that the leftmost two pins are ground. The next two pins (3,4) are routed through a SOT23 device that measures as a dual diode- most likely a dual Zener/TVS for ESD protection of comm lines. Pin 5 has a single channel TVS/Diode looking thing. That most likely means we have SMbus (a typical comm channel for notebook batteries) on pins 3 and 4, and a battery temperature on pin 5. Pins 6 and 7 remain mystery for now and pins 8 and 9 are the battery positive.
Next step is to try waking the battery up. We apply normal for it voltage (in the range of 3-4.2V per cell) and see if it “takes”any current. Nothing happens, no current is going in. Plan B-  put the battery back in laptop and observe signals on the pin. With the laptop powered by a bench power supply, we can see a notable surrent spike when battery is inserted, so something does happen. Voltage on the pins is now 12.6V, meaning the charger is trying to do its job but no current is actually making it in. Poking around with a scope, we can see activity on pins 3 and 4. And pin 3 definitely looks like an I2C clock, pulsing nonstop during the comm intervals, while pin 4 looks like an I2C data. Ok we’ve just confirmed 3 and 4 are indeed the SMbus pins and the battery is talking to the charger.
For more detail: Testing laptop battery: pinout, SMBus, charge capacityTesting laptop battery pinout SMBus charge capacity

About The Author

Ibrar Ayyub

I am an experienced technical writer holding a Master's degree in computer science from BZU Multan, Pakistan University. With a background spanning various industries, particularly in home automation and engineering, I have honed my skills in crafting clear and concise content. Proficient in leveraging infographics and diagrams, I strive to simplify complex concepts for readers. My strength lies in thorough research and presenting information in a structured and logical format.

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