Macbook Pro mid-2015: Power button = Dead Battery screen / no charge

The flex cable over the battery is the Trackpad IPD Flex Cable. It won't prevent powering on or booting except that you won't be able to use the Trackpad or the built-in Keyboard, plus the fan may run at high speed possibly causing the laptop to run really slow since the Trackpad temperature sensor won't be seen (not sure if the slowness occurs with the 2015 model).

Sounds like you have some other hardware issue, most likely with the Logic Board, but I would remove the internal SSD & adapter to see if you at least get video of a flashing folder with a question mark. That is a third party SSD since I don't recall any Apple OEM SSDs having any LEDs on them.

I agree the Battery is most likely bad. What is the battery condition? You can get this by Option-clicking the battery icon on the menu bar. If the condition is anything but "Normal", it should display something. You can also check the condition in the Battery System Preferences or the Apple System Profiler under "Power". If it says "Service Battery" (macOS 10.15.4 or earlier), then it indicates a hardware failure with the battery. If it says "Service Recommended" (macOS 10.15.5+), it could mean a worn out battery or even a failing battery.

If you have the 15" model, then check to see whether you qualify for the Battery Recall as mentioned in this Apple article (only a small number of laptops actually qualify...best to know if yours qualifies before having Apple examine it in case the tech overlooks it):

15-inch MacBook Pro Battery Recall Program - Apple Support

DGShuffle wrote:

• Using alcohol cleaning pads and compressed air, I cleaned any dust from the MagSafe 2 connection and the inside battery connections. I couldn't find any corrosion, at least on the visible areas of the logic board.

Liquid damage could also be a possibility. If you are not use to looking for corrosion, then it can be very hard to detect even with a magnifier since it only takes the smallest bit of corrosion between two of the smallest pins. Even someone with lots of experience can sometimes miss it. Plus if liquid made it beneath certain chips the corrosion may even be hidden and water rarely leaves a residue trail unlike some other liquids.

If liquid was spilled on the keyboard, then the liquid would hit the hidden side of the MLB anyway assuming it made it past the mylar sheet beneath the keyboard. I don't recommend removing the MLB as that is a major undertaking with it being very tricky to fit the MLB back into place.

Or it could just be a failing MLB with no damage. Unfortunately there is no way to know for certain without trying another battery, although I have developed a method of using the command line to monitor the battery's Full Charge Capacity in order to look for issues which are hard to confirm when people mention having poor battery runtime which don't show up in the Battery Condition or the Apple Diagnostics.

• I removed the battery and connected the power (same result). I noticed that, when connected, after a few seconds, the fans spin for about 7 seconds, then stop. Also the SSD blinks red once.

Fans spinning is not unusual when connecting power like that. What do you mean the SSD blinks red once?

DGShuffle wrote:

Next (and hopefully last), I replace MagSafe 2 DC-in board. I ordered a used one from eBay, expected this weekend. Once installed, I'll share an update here.

While I used to replace the DC-In Board on much older Macs, I've never (or rarely) had to on the 2015 Retina model. Usually there would be a visible issue on the external contacts, or actual physical damage or liquid damage.

I'll have to decide if I'm ready to attempt a soldering job on the logic board despite my lack of experience. 😕

Apple Logic Boards are very difficult to solder as the board acts like a heatsink and may require a mix of traditional soldering iron and hot air station. You would need to acquire a schematic & board view of the specific Logic Board in order to identify & locate components (and software to read the board view), plus you will need to be able to understand the schematics and Apple's power/charging circuitry. There has only been one person I've seen online who has explained it (LR), unfortunately the moderators won't permit posting details.

Those are all symptoms of a dead battery. To obtain battery service for your Mac, start here: Get help with your Mac laptop battery - Apple Support

Chrome is fine to use, but when you start looking closely at system temps, resource usage, and performance you must keep in mind that Chrome greatly affects all of these areas. That is the only reason I mentioned it. It is hard to get away from using a Chromium based browser these days.

CMM is where most people end up having all sorts of issues.

I misunderstood your earlier reference to the temps you were seeing since you referenced the heatsink at the time. CPU temps will be around 35C to 40C at idle, while normal usage will place the CPU temps more around 60C, with 95C - 100C when under extreme load. Battery temps should usually be around 30C, maybe as much as 40C when the system is under extremely load when the CPU is 100C.

You're welcome. I'm glad you figured it out. Thanks for following up.