Boots to apple logo then shuts off

Hey everyone,

I wanted to post here as I also fix iphones, ipads, ipods and provide micro soldering on basic level repairs such as charge ports, ps4 hdmi ports, ipod batteries, etc...

Anyways, I have a customer who brought their Ipad Mini 3 Wifi + Cellular in for repair. It needed the LCD Replaced. After replacing I plugged the ipad in to charge as it was sitting out in the cold and hot for many months since it was broken! It took about 45 minutes just to turn out. It was charging at 1.8amps close at 5 volts. Anyways, it turned on finally and had a passcode. Customer didn't remember it so he asked to restore it for him! So, I let the ipad charge and it took about 4 hours to fully charge from 0 to 100 percent and was working and it was staying on. The next morning I downloaded the ipsw and did it twice... I restored the ipad both in iTunes and 3utools and it was successful. Now it turns on to the apple logo at 0.42 volts for about 8 seconds then shuts off to 0.01 volts. When I press the power button again to turn it back on it repeats the same thing over.

I took the ipad apart and tested the battery with a multimeter and their are 4 solder joints on the battery itself. I have two readings and the battery is rated at 3.75volts. I tested the battery at 4.1volts and also 2.3volts. I also tested the charge port connector pin and I am receiving 5 volts.

Now, I am wondering if a new battery will fix the problem as its under voltage to go past the apple logo on start up. I am completely lost and I want to know if anyone with board level experience can assist me to get this thing working again! Please, no stupid answers like did you try putting the ipad into dfu mode and this and that.

I took proper measurements and need expertise help at board level to help me determine if you guys think its the battery being faulty! Like I said it was working great before restoring at the passcode screen. Restoring seems to hang at the apple logo screen and shut off.

Anyone help is greatly appreciated!

It also has no water damage and was sitting dead for almost a year

It's also about 2 - 3 years old

Thank you