95 crown vic charge issue

got up the othr day and the battery was dead,
Nothing new for me I figured I left something on. Jumped it and off I went. A week later same thing but this time I knew I didn't leave anything on.
have been driving it another week but the batter indicator keeps staying low. I mean when it starts it drops down to the l almost

If I'm not driving it and the lights are on < auto lights > and I hit the windows the lever goes down to L

I took it to have the alternator check and they sad the battery was good but real Low. and the alternator tested ok too.

Allot of corrosion on the terminals so I cleaned it and put protective spray on it. let it run for about 5 minutes

but the indicator still didnt go as high as normal.

Will try to drive it a bit to see if it charges it.

but worst case scenario how hard is it to change one?

Found some info on Autozone and it kept referring to tightening the screws to x lbs I don't have a torch wrench is that really needed?

The torque is not really critical on this. Just be sure the connections are clean and tight. You may need to charge the battery to see if it helps the problem. If the corrosion was bad enough to keep alternator from properly charging the battery, then a charge might be all you need if the alternator is indeed ok.