Battery not charging

[SteveS]

I mentioned this in the "what did you do to your" thread last week, but a week ago Saturday the Fiesta wouldn't start. Jumped it and drove it home, battery showed 20% charge. (original battery in a 2019). Put it on a charger and it charged up to 100%. Started just fine. Wife drove it to work and stuff all last week. We went out of town for Thanksgiving in a different vehicle and got home yesterday. Wife drove the Fiesta to grocery shop. This morning it wouldn't start. Put the charger on it and it showed 9% charge. So evidently it's not charging. In looking at the alternator, I pressed on the belt. It can be pressed down well over an inch. Is it supposed to be that loose? Never really examined it before.

 

[Capri to ST]

I mentioned this in the "what did you do to your" thread last week, but a week ago Saturday the Fiesta wouldn't start. Jumped it and drove it home, battery showed 20% charge. (original battery in a 2019). Put it on a charger and it charged up to 100%. Started just fine. Wife drove it to work and stuff all last week. We went out of town for Thanksgiving in a different vehicle and got home yesterday. Wife drove the Fiesta to grocery shop. This morning it wouldn't start. Put the charger on it and it showed 9% charge. So evidently it's not charging. In looking at the alternator, I pressed on the belt. It can be pressed down well over an inch. Is it supposed to be that loose? Never really examined it before.

Can a battery get too old and weak to charge? I was going to say I would suggest replacing the battery because it's 4+ years old which I'm sure you've thought of, but if there is a charging problem you don't want to weaken a new battery.
Whenever you fix the problem, or determine that it is just that the battery is too old, I would definitely replace the battery. I just do it automatically at 4 years to be on the safe side, because I have read of all sorts of odd things happening to the car with a weak battery that don't on their face seem related to that.

 

[SteveS]

Just replaced the battery. The old one charged up to 100%, then I tested the charging with voltmeter. But two starts had the battery down to 50% capacity on the charger's gauge. And even with everything electric I could turn on in the car, the battery was charging pretty quickly at idle. Voltage was up to 15 volts from the alternator, though it appears the voltage regulator controls things pretty tightly because it fairly quickly drops down to around 12.9-13.0.

Took the battery to O'Reilly and it tested bad.

Unfortunately the only choice was a pretty mundane battery at a pretty high price.