Microsoft Surface Pro 4 battery pinout

Submitted by lululock t3_124rrro in DIY

Hi,

I had the opportunity to salvage a Surface Pro 4 with a swollen battery.

Of course, I will not use it with that battery. I'd like to replace it but I know the cooler design flaw will affect the new battery as well. I also can't seem to find reliable batteries anymore.

So I figured that maybe I could use some external battery cells, in the form of 18650 cells. I don't mind it to be bulky. I just want it to be reliable and easily serviceable (and flip the middle finger to Micro$oft in the process).

But, I need to understand the pinout of the current battery in order to build a substitute.

Here's a picture of the connector on the original battery.

From what I can see, the connector is a flexible PCB with golden pads on it. There are 2 positive pads and 2 negative pads, I assume one for each battery cell.

For the rest, I don't know. They are probably communication pins used by the battery circuitry to indicate the number of cycles, current charge and current capacity to the motherboard.

Has anybody tried to understand how the Surface communicates with its battery ? I'd like to try myself but I have limited equipment and knowledge but I also want to avoid pouring power in the time bomb that is the current battery.

Do you think the Surface will use the supplied power if none of the communication pins get a response ?

Worst case scenario would be to remove the battery and power the Surface through its charging port with a "Surface to Type-C" adapter and just plug my powerbank into it. But I'd prefer creating a substitute to the original battery. Makes for a more interesting project.

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Comments

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Spritzer2000 t1_je0i9up wrote

I don't have the pinout to hand, but it's fairly moot as you would need to move the BMS from the old battery to the new. Unless it handshakes, it won't receive power. Microsoft surfaces don't like receiving power at all without the BMs connected

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lululock OP t1_je0j663 wrote

Yeah, that's what I was afraid of...

Any way to rip the BMS from the old battery without setting it on fire ?

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Spritzer2000 t1_je0t4f9 wrote

Wouldn't be something I'd risk to save a couple hundred tbh. If the swollen cell is far enough away from it, maybe? If its badly ballooning, don't bother.

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lululock OP t1_je0u634 wrote

The BMS seems to be located right between the cells. If I cut short each cell wires, there should be no short... But the cells doubled in thickness, I'm even afraid to remove them from the casing.

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Spritzer2000 t1_je0vv80 wrote

I wouldn't bother attempting to create your own battery. Personally I would attempt to buy a battery from a reputed vendor (original is better but does not have to be), and if you have prior experience dealing with fire risk batteries, go full send next to a bucket of sand.

If its your first time, pay a reputed repaid shop, and start off with another, less risky repair

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lululock OP t1_je0wt7o wrote

The tablet is already disassembled, thanks. I already dealt with similar devices to not break stuff while attempting a repair. I've just never dealt with such a bloated battery.

The idea was to fix that inherent design flaw the Surface Pro 4 has : A massive part of its heatsink is covering the battery and transfers heat to it, damaging it the more the Surface is used.

If I replace the battery, it will do it again in a few years if not sooner due to lower quality cells.

Buying good quality 18650 and making 3D printed parts to fit them outside the casing will cost less than a replacement part from Ifixit...

I not only want to fix it, but I want it to last longer.

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Spritzer2000 t1_je0zb2o wrote

Ah excuse me I misunderstood the original intent. I can't pretend I understand your reasoning, as it sounds like a very non portable solution for a device that was sold on the basis of portability.

I would probably recommend buying the replacement battery and attempting to remove BMS from that rather than mess about with the spicy pillow

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lululock OP t1_je1010x wrote

You're right... I guess I'll salvage the BMS from another dead battery which hasn't expanded yet. I'll ask a few repair places around. Maybe they could even strip out a BMS for me.

But then comes the part where I'll solder new cells to it. Do you think it will get the extra capacity of 18650 cells ?

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Spritzer2000 t1_je151mq wrote

If it's done properly, I don't see why not. The only thing that might get in the way will be if there's an individual bms system in each cell that handshakes with the "central" system. I haven't actually cut into batteries in a while, generally only replace them

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lululock OP t1_je163p2 wrote

I've found a picture of a BMS someone took appart.

The left one is from a Chinese copy but the right one is the original LG one. Looks like both cells would connect to it. Comments say that the original BMS has a temperature sensor and charging control and that's why some Chinese copies won't get recognized by the Surface.

I think I'm getting somewhere with my idea.

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thoraway97 t1_je1jfz6 wrote

Based on the pins in your other picture, clk and data are probably an I2C interface, int is for sending hardware interrupts, not sure about "det". If you have access to an arduino or something, you might be able to try reading the output from a working BMS and then reverse engineering it for your own battery, but that's a bit of time and effort compared to a OEM part. Maybe some sort of insulator inserted to block the heat from the fan instead?

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lululock OP t1_je1k5sw wrote

I planned to get a working BMS from (preferably) a non bloated battery to minimize puncture risks.

There's absolutely no insulation from the heatsink and the battery. Microsoft did put a huge chunk of the cooler on top of the battery (I strongly believe it has been done in propose). Nobody with a sane mind would do that but yet, Microsoft did it...

I think that I'll try to solder 18650 cells to the original BMS and see how it goes. If it does well, no need to reverse ingeneer it. If not... I guess I'll have to acquire some knowledge first to do it myself.

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