Using this app

https://play.google.com/store/apps/details?id=com.macdom.ble.blescanner

the device shows up and reports Generic Access Service, Generic Attribute Service, Device Information, and Unknown Service.

When it connects, the LED lights, then stays on for a few seconds, then shuts off. The BLE app remains connected. Measuring the cell voltage at the terminals I start at 3.030 (measured with Fluke 79III) and drop Immediately to 3.004 then back up to 3.006 when the LED goes off. When my phone sleeps in 10s the app disconnects and voltage rcovers to 3.030.

Connecting with your app shows a voltage drop to 3.007 upon connection then quickly going up to 3.022 when it reboots then 3.030 when rebooting is finished so I don’t think it’d be a brownout.

I can bring it into the lab tomorrow and see if I can get a roll trace and possibly a current measurement on one of our nicer scopes.

P.S.: So glad you used nice inserts for the screws so taking it apart like this doesn’t mess things up.

P.P.S.: Not sure how you have things wired up, but if you’re trying to get a debug serial port, sparkfun has a microSD breakout https://www.sparkfun.com/products/9419 which lets you get at the pins in the microsd connector with a minimum of hassle.