Testing car battery / alternator questions

My 2001 Nissan Sentra suddenly out of no-where will not start anymore. I am trying to diagnose and learn how to solve this problem myself for educational purposes. Here are the details I have diagnosed:

-The car will not turn over (no chug-chug-chug noise). When I turn the key, I hear just a click.

-If I connect my dead batter to working car's battery with jumper cables, my car starts fine

-I unhooked my bad battery, plugged it into a trickle charger overnight and put it back in the car. I checked the voltage reading 24 hours after charging and it reads 12.5-12.6v (which at first I thought meant my battery was okay?). However, when I put the battery back in the car, it still wont start.

-If I boost the car with jumper cables, and check the voltage of the car while its running, I get around 15v with nothing on, and if I turn my headlights, heater, and turn up my stereo loud, it goes down to about 14.8-14.9v.

Questions:

1) Does my voltage test while the car is running verify my alternator is okay? Ive been told to check the batter voltage while the car is running and if its above 14.7v while the car is running ,then my alternator/charging system is functioning properly. Anyone confirm or deny this for me?

2) My motomaster car battery charger has a 2A/12A/75A settings. The

75A setting even says "car boost" or something to that effect. When I hook up the car battery charger up to my battery and set it to 75A, the car will NOT start this way (It did a little chug-chug once, but usually just makes the click sound). Is my motomaster car battery charger just not powerfull enough to boost my car? Or is there something else going on here I am not aware of?

Is the problem just my battery is dead? I want to make sure Ive done all the tests to verify that it is my battery that needs replacement before I go out and buy one.

Reply to
quentinmacdougall
Loading thread data ...

A dead battery will show voltage. But! Not enough amperages to start the car.

Did you check the voltage with the jumper cables on? Make sure you are only checking your voltage with your own battery connected and engine idling.

I recently replaced my alternator on my 2001 Sentra. The battery light in the dash never came on to tell me the alternator wasn't charging. I got an alternator at a scrap yard for 110$. Now the charging light is on when the car is not running as it should and disappear with the engine running. At idle. It's charging close to 14.7v. The Nissan book says between 14.1 to

14.7 is good. There are also fuses you can check just beside the battery. The cover will tell you which one.

Also maybe! Something is defective in your car and draining the battery when it's not running.

Correct!

A very dead battery will take a while to start a car while been boosted. At first It seem it just suck the power for itself.

Check all your connections first. Battery, Alternator, Starter and ground. No greenies...

I have the service manual in PDF, would you be interested? It's not that big.

Reply to
Ernest

From your description:

- With the engine running, no jumper cables, electric loads, the voltage reading indicates that the system is charging and probably too much. 15V is on the high side. My car, with full load, puts out 14.1. The battery I just replaced was 7 years old.

- A battery after being charged for 24 hours even on trickle charge, should be able to start the car.

- The 75A booster setting in your charger is just that... a help for the battery to start the engine. If the battery is defective, the 75A setting may not be enough.

- I would just replace the battery. I recently replaced mine and after investigating about batteries, I decided to go with the batteries sold at walmart, made by Johnson Controls who makes the DieHard batteries for Sears and many others.

Good luck!

nucleus wrote:

Reply to
AS

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.