TL;DR: Perhaps this doesn't sound like a RE post at first, but it's kind of moving in that direction. Essentially, I replaced the battery in my Surface laptop with 2x different new batteries, and they charge perfectly fine but the laptop won't run off them.

I really like my Surface Laptop (1st gen), but was frustrated by the fact that the battery was all-but dead, so I decided to take the plunge and replace it. For those unaware, the surface laptop (1st-2nd gen) are not designed to be serviceable -- they are glued/soldered together. It is possible to open with a scalpel, as long as you are patient enough. There are screws and normal laptop connectors once you pry the keyboard from the base, luckily. All this was fine and good, and I was able to install the new replacement battery, however it didn't take me long to realize that while the battery would charge from the original ~30% to 100%, as soon as I removed the power connector the computer would shut off. So I took the laptop apart again, and double-checked the connections, but I couldn't get it to start with just the battery. To be clear, it won't start off battery AT ALL (no POST/BIOS), so I find it hard to believe that this is anything but a hardware issue. Here are the things I've tried:

-Verified that battery maintains correct voltage -Purchased 2nd battery, observed same behavior -Uninstall/Reinstall battery driver -Updated BIOS -Checked BIOS to make sure there weren't any weird settings associated with battery -Verified all "Smart data" was present/nominal using batteryinfoview -Attempted "hard reset," by removing battery and depressing power button for ~1 min to discharge caps etc -Manually made connection between battery and motherboard (without connector)

Right now I have three leading theories:

  1. The "Smart" behavior of battery (or motherboard) is preventing current from being drawn from the battery.
  2. The "switch" that determines when to switch from AC power to battery power is malfunctioning (not even sure if this is a real thing)
  3. Microsoft prevents anything but the original battery from powering the unit
  4. Motherboard got partially fried during disassembly/reassembly

For 1), I'm currently trying to to investigate. The battery has six terminals: +, -, Det, Int, C, D. I believe that C and D serve as the communication BUS, and am trying to discern the purpose of Det/Int. I suspect that these tie either to HIGH or LOW indicating the presence of the hardware, but at this point I am unsure. I have attempted to provide power to the terminals using my variable DC power supply and was NOT able to power on the unit, which to me indicates that there is either some internal "switch" that prevents current being delivered, or that this part of the motherboard is indeed dead. But because the battery charges just fine... it's difficult for me to see the latter being the case.

For 2), I noticed that there are a LOT of wires in the cable that runs from the power connector to the motherboard (~20 or so), and while I was careful to remove this cable carefully, I wonder if there is a cable that exists in there that is a "sense" cable that detects the presence of external voltage and tells the motherboard to switch over to battery accordingly. Again, I don't even know if this is a thing.

For 3), I assume I'm completely boned, as the circuitry is opaque due to the multi-layer PCB.

For 4), I cannot see where the battery connections are going on the motherboard because they all appear to go to the inner layers of the PCB. I've looked around the mobo for signs of a blown transistor/IC, however I've been unable to detect anything. Unfortunately, I destroyed the old battery while removing it, so I cannot go back.

I have access to fancy diagnostic equipment through work, and am accomplished at SMD soldering etc, so pretty much anything is on the table. Literally any help would be great...Thanks folks!



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