Bad alternator or battery?
Drifting
Joined: Dec 2017
Posts: 1,663
Likes: 417
From: Central Texas
Do you have a multi meter? If no, buy one. If yes, check voltage of batterry after fully charging, should be close to 13V. Then start the car if possible. At idle, record the amount of volts at the battery. Then check again at 2500, and 3500 RPM, voltage should rise if alternator is charging.
How old is your battery? If over 3 years, buy a new one. Good luck.
How old is your battery? If over 3 years, buy a new one. Good luck.
Le Mans Master
Joined: May 2003
Posts: 8,877
Likes: 3,556
From: Fernandina Beach FL
2023 Restomod of the Year finalist
2020 C3 of the Year Winner - Modified
Some food for thought-
When the battery goes bad- the alternator is often overworked- trying to charge a battery with dead cells-- then that takes the alternator with it.
On the other hand- a bad alternator wipes out a battery by continually not charging it back up....
It's a catch 22- I see so many find that one is bad- think they have the problem solved- only to come back and replace the other.
Just sayin-
Richard
When the battery goes bad- the alternator is often overworked- trying to charge a battery with dead cells-- then that takes the alternator with it.
On the other hand- a bad alternator wipes out a battery by continually not charging it back up....
It's a catch 22- I see so many find that one is bad- think they have the problem solved- only to come back and replace the other.
Just sayin-
Richard
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
First, check to see what voltage is present at the battery (or at the primary power lug on the alternator to ground point) when the car is running at idle and warmed up. It should be near 13.5 vdc. Then turn off the engine and check voltage again. It should be a bit above 12 vdc
With battery [supposedly] fully charged by alternator and car NOT warmed up, turn on your headlamps with Hi-beams on, then turn ignition to START. Watch brightness of headlamps as you turn the ignition key. If the lamps significantly dim when starting, the battery has lost significant 'capacity'. Can't say that it is 'bad'...but it is suspect.
You could remove the battery and have it checked somewhere. But they would need to do a real 'load test' on it. Keep in mind that whatever store you take it to has a GOAL of selling you a new battery....
With battery [supposedly] fully charged by alternator and car NOT warmed up, turn on your headlamps with Hi-beams on, then turn ignition to START. Watch brightness of headlamps as you turn the ignition key. If the lamps significantly dim when starting, the battery has lost significant 'capacity'. Can't say that it is 'bad'...but it is suspect.
You could remove the battery and have it checked somewhere. But they would need to do a real 'load test' on it. Keep in mind that whatever store you take it to has a GOAL of selling you a new battery....
