Welcome to Android Central! Are you saying that you forgot the password to your Desire 626s? Or was it already password locked when you got it at this yard sale? If the latter, then we can't help you, because even if you did a factory reset, you'll need to know the prior owner's Google account and password to even get to the Setup Wizard. That's Google's Factory Reset Protection in action.
Maybe we can help you with your other phone. Which one is it? Does it have a removable battery? If so, try a new battery.
It can also help to see some battery stats. Charge up to 100%, then let it drain to 20-30% with normal usage, without charging in between. Then show us:
1. The main
Settings>Battery screen.
2. The fullscreen battery graph screen (which shows Awake time and Cell Signal Strength).
3. The Screen category (to see total Screen On time).
4. The Cell Standby category, if present (to see Time Without Signal).
http://forums.androidcentral.com/amb...d-central.html
You might have to install a 3rd party battery monitor, like GSam Battery Monitor, to get the Cell Signal Strength graph.