my ultra has been getting really hot when charging. i am using the charger that came with it and also have used a replacement charger and same thing. it gets hot when i am playing music or using it a good bit. in the last hour it went from 60% battery to 3% and all i was doing was texting and reading email. i have never had any problems with this phone other than the occasional glitch that we all get.
As this is your first "major battery problem" with this Droid, it would be a wise move to think possible app problems. From reading your post you may have done a recent app install or one or more of your apps may have updated and change the app's settings. This could account for more heating and power drain on the battery. That would cause Wi-Fi or data to run more as the app is updating information or more run-time use. Think about any apps you may have installed or settings that have been changed. Go to your device settings and then battery to see what is using up the most power and run-time. Then shut down or change that app's settings. You could also start the phone in Safe Mode and see if this helps your heat and battery issue to go away.