If you have a MacBook Pro A1286 (15.4″, Late-2008 until Mid-2012) and want to replace the battery, you must be aware of the specific battery in your device. In 2011, for some reason, Apple decided to switch from the battery model A1321 (73 Wh) to model A1382 (77.5 Wh). While the form-factor stayed the same, Apple changed the connector and pinout.

In the above picture, the A1321’s connector is the top one with the A1382’s at the bottom. Notice the small “+” and “-” marks on the plugs which indicate the changed polarity.

If you search for the model numbers and the word “battery”, you’ll soon end up on this page or probably this one.

As you can read there, the pinout of one battery is:

[+12] [+12] [+12] [SCL] [DET] [SDA] [GND] [GND] [GND]

while the other one is:

[GND] [GND] [GND] [SCL] [DET] [SDA] [+12] [+12] [+12]

(SCL = SMBUS_SMC_BSA_SCL, DET = SYS_DETECT_L, SDA = SMBUS_SMC_BSA_SDA)

Here is a photo of both batteries where I’ve marked the +12V lines (left: A1382, right: A1321):

If you are comfortable with using a soldering iron and doing some delicate soldering, you can “easily” (sort of) swap the connectors and the 12V and GND wires. The 3 wires for the 12V supply and the 3 GND wires are shorted, so they’re not going to different cells and it’s not important whether you swap 1-2-3 with 7-8-9 or 9-8-7 or 7-9-8 or 8-7-9 or … (and vice versa).

I DON’T TAKE ANY RESPONSIBILITY FOR WHAT YOU’RE DOING TO YOUR HARDWARE. Just because it worked out fine for me, doesn’t mean it will work for you.

Once you’re done, it might look like this:

Time to plug it into the MBP. Watch out for funny smells, smoke or the battery heating up. But if everything went fine, you should be able to turn on your MBP just fine.

Once it finished booting up, head into the system information and check the battery info. For me, it looked like this:

SUCCESS!

Bonus Picture

This is the controller PCB of the old A1321 battery:

The three Microcontrollers (U-label, all on the left hand side) on there:

• U200: TI bq20Z45 Charging Controller
• U301: CJG W — TI bq29410DCT Secondary Over-Voltage Protection
• U302: CBZ — TI TMP102 Low-Power Digital Temperature Sensor with SMBus