Testing laptop battery: pinout, SMBus, charge capacity

Introduction:

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

Patient all hooked up

Patient all hooked up

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:

Battery connector details

Battery connector details

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.

That seems to indicate it is alive, but too discharged to allow for charging- most likely staying in precharge mode with a large series resistor limiting input current to very low values. Leaving things alone for a bit and checking back in a few hours, the power supply current went up drastically from about 0.5A at 19V to 1.5A. That may be a good sign- battery is now taking current. Voltage check confirms that- we are now at 11V and rising, meaning the fast charge constant current phase is on, and the battery is finally charging. Well, might as well let it finish. Once the laptop’s charge indicator goes from yellow to green and power supply current drops, we can start the tests.

First check is battery voltage and once again it is 0V. At the same time, I can plug into the laptop and it stays powered. Something else is going on- time to check if we are missing anything. It then occurs to me that some batteries have a signal called System Present, and only allow charging/discharging if they see that signal. Well, we still have pins 6 and 7 to figure out. Measuring the pin to ground resistance in and out of system we see that the laptop pulls pin 6 to ground when battery is inserted. A quick test with a resistor between pins 6 and 1 confirmed the guess- battery voltage appears on the positive terminals.

In  the absence of proper  connector, diodes will do

In the absence of proper connector, diodes will do

Now we can run tests on the bench. First we connect a TI EV2300 interface

TI EV2300 USB to I2C/SMBus adapter

TI EV2300 USB to I2C/SMBus adapter

and wire its SMB Clk, Data and ground to the battery. We then use TI’s evaluation software to look at the reported data. It is not known if the chipset inside the battery is indeed the part this program was written for or if it’s even a TI chipset in the first place, but luckily SMBus standard defines the base set of registers everybody has to support:

TI Smart battery interface GUI

TI Smart battery interface GUI

From SMBUs data we can tell that the battery cells are healthy, well balanced and fully charged. The pack saw 6 discharge cycles and thinks its full capacity is 4400mAh, just as indicate don the label. So far so good. Next we apply constant current load and run a discharge cycle to see how much capacity we can get out of the battery. Running at 1.5A with a 4.4 AH capacity, we should see close to 3 hours of runtime.

 Results:

After 2.5 hours or running at 1.5A, the battery reported 0% capacity. It also adjusted full charge capacity down a bit to 4Ah.

Battery state at the end of discharge, starting charge

Battery state at the end of discharge, starting charge

That’s the amount of charge internal gas gauge counted going out during the last discharge cycle. So we have a 4Ah pack, out of 4.4Ah initial design capacity, or about 91% state of health.  Seems like a reasonably healthy battery that should provide service for a while.

Links and resources:

For those interested, here are the things mentioned:

Pinout: 1,2 GND, 3 SCL, 4SDA, 5 Temp?, 6 SysPresent, 7-??, 8,9-BAT+

TI EV2300 http://www.ti.com/tool/ev2300

TI bqEasy software http://www.ti.com/tool/bq20z45-r1_bqeasy-sw

 

16 thoughts on “Testing laptop battery: pinout, SMBus, charge capacity

  1. Pingback: Testing laptop battery: pinout, SMBus, charge capacity « adafruit industries blog

  2. I have the same battery and terminals on a satellite A200-1BW. The old battery appeared to have died so i bought a new one,10.8v 4000mAh. It started off out the box at 6%. after leaving it for a few hours I checked again and still 6%. It say’s “plugged in,charging” but it obviously isn’t. how can i get it to accept a charge? I tried all the usual take everything out and turn off techniques. plus the deleting the old driver.
    pin7 i notice as a 1.4v charge coming from it in the laptop.

    “please ob1kenobi…your my only hope!”

  3. is it ok to charge the battery from external source only through pin 1 as -ve and pin 9 as +ve?

    which is (-ve pin 1) in your photo? the very left?

    • It should be fine if you run at lower current, something like 1-2A. I don’t know exactly what these pins are rated for. The left one (the one I connect black wires to) would be ground, it’s near the silk marking JP8800 on that picture

  4. Yesterday, while I was at work, my sister stole my iPad and tested to see if it
    can survive a thirty foot drop, just so she can be a youtube sensation.
    My iPad is now destroyed and she has 83 views.
    I know this is entirely off topic but I had to share it with
    someone!

  5. Hello dear, very useful your post! I have two simples doubts about measuring laptop batteries with a multimeter. Considering a normal battery, which is not depleted:

    First: how to measure the voltage or current charge, matching with computer percentage? For example, computer says that the battery has 40% charge, how get this with a multimeter?

    Second: how to discharge a laptop battery by the terminals, which terminal may I use for it?

    thanks for attention!

  6. Charging voltage on 10.8v 4400mAh 6-cell Li-ion is only showing 8.9v, minimum for charge is 10.8v as indicated on battery label, so any ideas on why laptop is not charging at correct voltage?… Increase/decrease amp or wattage on ac adapter maybe?…have the same “plugged in, charging” issue as rich above, but sits at 8% when it came out of box at 43%. Ran HWMonitor to find out if battry was good because I don’t have all the tools to check charging voltage. Even OEM replacement ac adapter wont charge either original dead battery or this one I am trying to charge now.

  7. Can i connect 3 battery 3.6 to have 10.8v with port 1,2 and 8,9 directly ???!! I will disconnect them and use external charger.

  8. Hi,
    why there is two positive pins (8 and 9)? is it means this battery has two pair of terminals? for example one for LCD and other for computing resources.

  9. i will like to know the following, i have seen many laptops that their charging circuits are bad. So, voltage was tapped from a capacitor to supply charging current to the battery. Which of the pins in the charging terminal charges the battery? How many volts can one supply to the battery to bypass the charging IC?
    The 10v above, is it for powering the laptop or charging the battery?

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>