Re:Battery Voltage

Hi all,

Hoping to get a little bit of help figuring out if my battery voltage is normal.

disclaimer: car is in use - hasn't been sat standing.

Battery measured at the terminals at 12.4v (engine off)

Battery hovering around 12v with engine ON, lights on and radio at idle.

The battery is fairly new (8 month old Yuasa with 3yr warranty) - wondering if maybe my alternator is a bit pathetic?

Anyone else got any insight into this? The reason I ask is that I am changing back to my old headlights and when on high beam at idle, they flicker and the voltage at the terminals drops to 11.95v

EDIT: Voltage drop to 11.6v at the terminals when lights are on high-beam at engine idle - this can't be right surely?

I assume this is a Gen3

A battery that's charged but without load should be around 12.6 to 12.8 volts.

With the engine running the peak voltage should be up around 14.6 volts but anything over 13.8 volts means it will charge.

Gen4 have an intelligent charge system which "turns off" the alternator so you will see different voltages

So does should like a possible alternator problem.

Sent from my Pixel 2 XL using Tapatalk

Thanks Martin - yes this is a Gen 3.

OK - so it looks like the battery is under-voltage by a long way - as you say, this points to an alternator issue, given that the battery is not that old.

I even went as far as to hook it up to my other battery (in parallel) which helped...but did not keep the voltage above 12v (hovering around 11.8v with high beam on).

Martin's spot on.
It appears to be the alternator, my G3 sits at 14.2 volts with or without the lights on according to the cheap usb display thing. Drops to 12.5 with the engine off, but it's an old (but still working) battery.
Mike

As said above, the battery voltage should be above 13.2V when the engine is running and if it isn’t the fault is probably the alternator.
Before removing/repairing/exchanging the alternator I would:

- Measure the battery voltage at higher revs, not idle, e.g., at 2000rpm.

- check the connections to the battery and remove any corrosion, dirt, ... and re-measure the voltage at the battery at 2000rpm.

- Charge the battery with an external charger and check how much energy goes into the battery, there are some chargers that measure this or you can measure the battery voltage while charging every 30min). Then recheck the battery voltage at 2000rpm.

The reason I would do this is first, because it is not much effort and secondly to verify an alternator failure. Because you wrote that the lights are flickering in idle and with flickering I would think that there is at least some charging and I did experience new batteries being defective in the past and also corrosion at cable connections that lead to interesting voltage measurements.

I would suspect voltage regulator , which is built in to the alternator on a car ..(motorcycles are separate , so a touch easier to deal with ..money wise.)

However get the battery checked first as said , it could be the voltage is fine but the cranking power is down , so it takes a struggle to replace charge ....
I have a few m/c batteries that sit at 13. 4 v fully charged but won't start a bike....
( they power the electric fence though!)
That'll need a drop test ....but I would go for alternator / reg/rec.

But again as said disconnect the leads and make sure the earth connections to battery and body are good.