Welcome to Android Central! My guess is that it has to do with a change in how the battery info is accessed in Lollipop. The battery widget that you installed probably isn't compatible yet. Try emailing the developer of that widget and ask if there are any Lollipop compatibility issues.
Lockscreen widgets are gone with LP.
Alerts now show on lockscreen.
Find a battery app with alerts!
I use Battery by MacroPinch.
Go to Settings/Notifiations ON.