First, it's not uncommon for the gauge to drop below 13 or go well above 14. The charging system is supposedly "smart". Seeing swings in the gauge is not unusual.
In your case I think there really is an issue if you are getting the "Check Battery" light.
The symptoms do sound like either a failing tensioner or oil/coolant is getting on the belt causing it to slip.
New alternators are known to prematurely fail but that wouldn't account for the rise in temperature.
In your case I think there really is an issue if you are getting the "Check Battery" light.
The symptoms do sound like either a failing tensioner or oil/coolant is getting on the belt causing it to slip.
New alternators are known to prematurely fail but that wouldn't account for the rise in temperature.