Hello everyone, I recently had a problem where my car loss power and I had to change the battery. With the new battery, my car isn't charging the new car battery when its idling, it only charges when the car is rev'd up or has gas pedaled. Could it the fault be with my old 80,000 mile serpentine belt or is it something wrong with the alternator? Thank you in advance

 

What is the voltage across the battery when the engine is idling? What is the voltage across the battery with the engine off?

 

Good call, look at the charging voltage, assuming you know how to use a multi-meter. It should read 13+ volts. Good luck.

 

Thank you this is what i saw in my video recording.


1. engine off. battery started at 12.65

2. started engine and battery level went down to 11.26 lowest. and peaked at 14.30 after starting

3. battery leveling started discharging and went down to 13.70 and downward after 4 mins. ( I have a feeling it will still go down which is the main part of my concern)

4. When i press the gas throttle. the level did go up a tiny bit. like 13.71, 13.72, 13.73, 13.74, 13.75....

5. battery went down to 13.20 after i turned off engine. and when i check again a few second later it went down to 12.90

Is this considered normal range ? also i had everything off, no extra lights, fans, radio. What is the reasoning for the discharging battery volts and is this considered normal.

Thank you for any help!

 

Honestly seems almost normal numbers all around except my Tundra and 350 stay around 13.8 to 14.1V for roughly 15min then taper to 13.6 - 13.3v.

However, if it was driven for 30 minutes turned off and this test performed, it could easily quickly drop to that 13.6 - 13.3V number.

Some are having issues w parasitic loss where the battery drains while the car is off. Mind you a typical good long life battery is only 4 to 5 years. Shorter in hot climates and short drives.

 

Thank you! After a few test the engine start voltage is now peaking at 12.9v - 13.2 ish. After driving for 30+ mins the battery voltage is between 12.45V-12.9V.

Would this indicate that my alternator is going bad? This is a new battery and i checked to see if there's any parasitic loss but i can confirmed its negative for that.

 

Check out this video, it may point you in the right direction

 

What I didn't clarify was cold start vs hot start after driving for 30min.

Cold start >13.8v for 15 to 20 minutes.
>20 minutes = 13.3 to 13.6
Off 2 hours ~ 12.7

Does yours conform to this?

 

Thanks!

However, I would caution anyone following this verbatim as the times I've reconnected the battery a giant spark flies. That implies an amp meter would be sinking >10 amps and although most have a fuse, it's a possibility the meter could be damaged.

Adding to this, our cars have a hood sensor. it needs disabled.
Upon battery reconnect there is a power distribution computer on the CAN bus that wakes up things like the security system, the immobilizer, and various other computers. In short, you can't just disconnect the battery and get accurate results.

The car must go from a normal engine running mode, ignition off, then system shutdown. In addition to this, every two weeks of being asleep, these cars shut down additional systems to minimize parasitic drains on the battery. As I know it, there are 3 different shut down phases.

The work around is this. Don't disconnect the battery. Grab some test leads good for 5 AMPs or so. Secure hood and door sensors so car believes all is secure.
* Attach one test lead to a body ground preferably the same place the oem lead goes like the body or engine ground.
* Loosen the ground post clamp bolt. Do not disconnect.
* Place your meter in Amp mode, configure settings for at least 1Amp.
* Place the other meter lead on top of the negative battery post and don't loose contact. Lift the ground cable away from the post and watch the meters current. Clamp the lead to the battery post and do your diagnostic work.

That's it.

Tag #2IS Electrical Troubleshooting

 

morning Cold start it ranges from 12.9v-13.7v

after driving for over 20 mins. hot start goes from 12.5-12.9 usually, but sometimes it does go to like 13.3v or so.

Off 2 hours later - it ranges from 12.59v-12.7v

When i do press the gas pedal it does go up 12.9v - 13.8v


It seems like the voltage change is really random. For now the battery seems okay at the end of the day but its because this battery is 2-3 days old

My previous 5 month old battery had issues when i was driving. I loss power to the steering wheel and when i restarted the engine the car wouldn't turn on. I had to jumpstart the car and after letting idle for 30 mins the car shut off by it self. I then checked the battery voltage and it was below 11.5v.

I then purchase this battery and began to monitor the voltage where i realize there something going on with the voltage possibly thinking theres issues with the alternator. Thank you again

 

Take a look at this video from the Car Care Nut. I believe your readings show the alternator is working properly.

 

@Protholl
Great video. Thanks for sharing

 

Changed the alternator and everything is back to normal. Could have be volt regular could have been the brushing but I’m not sure.

 

Was going to say bad connections lead to erratic spikes/dips in voltages as do slipping belts (slip under load), and if those are resolved, replace alternator.

I suggest anyone who wants to keep a loose eye on system voltage buy one of 12V USB car charger w/Voltage read out.