Nope not a problem (anymore) but just something I wanted to share with you. I bought an XT894 of Ebay, apparently from an XDA member. The phone is unable to register the SIM. So I thought of buying a new daughter board and swap it out. Then I thought of just swapping it with mine just to be sure. I did, but to no avail. While testing I accidentally used my battery in the Ebay Droid. After the swap I placed the batteries back. The phones kept on working. But one of the batteries wouldn't charge (my own Droid with the battery I accidentally put in the Ebay Droiid). When I plugged in the charger, the phone started charging from 5% to 100% in 5sec. But the phone wouldn't boot. I left it on the charger for a night, also didn't help. Then I thought of soldering a factory cable and SBF the SOB. Yep, that also did not work. The same thing happened, you plug in the charger and it goes from 5% to 100% in 5sec. After that I just ordered another XT894 with a cracked screen. The mainboard can be used to fix the one I bought of Ebay. The battery can probably fix my own Droid.
Yesterday I decided to swap batteries again. I was hesitant because of the risk of killing both batteries. But for some reason Battery A works in Droid B an battery B works in Droid A. I charged both, drained both 'till they turned off. And now both are on their second charge. In short, both Droids seem to be working well after I swapped the batteries. I searched everywhere but could find no report of this. That's why I'm posting it. As you can see I tried everything I could think of. Nothing, noooothing helped.
The next step would be swapping the batteries back again. But I won't be doing that. I had to go through 4 days without a working phone.
Just thought I'd share. An apparently dead battery isn't always dead. Even when the factory cable doesn't seem to work.