donkinuts

iTrader: (3)

What purpose does the battery meter serve? Would 8 volts mean that the battery is nearly empty? I just got my new '08 two months ago, and was expecting to see the meter maxed out, but it's not.

davidv

iTrader: (2)

I think you mean the voltmeter.

The voltmeter measures charging-system performance. With normal alternator/voltage-regulator function, battery voltage is maintained at 14.0 to 14.5 volts. In the event of alternator-system failure, voltage will be low and continue to drop as the battery discharges. In the event of an "overcharge" condition, the voltmeter will climb above its normal zone.

dhays

iTrader: (10)

I'm pretty ignorant when it comes to 12V circuits (or any type of circuit for that matter) but the Voltmeter isn't a "battery meter" but measures the voltage difference across a circuit. You battery is nominally 12v, but fully charged is probably closer to 13v. All that means is that the potential difference across the terminals is about 12v. The Voltmeter isn't like a fuel gauge for the battery.

When your car is running, with all accessories off, and the rpm is up at cruise (maybe 2000 rpm?) you should see 12-14v. However, to be honest I haven't paid much attention to my Z's voltmeter to see what it typically reads.

When you turn the key on, with no accessories on, the voltage that you see should be what the battery's voltage is at that point. It should be around 12v. As you start the car, it will drop significantly because of the amps being pulled by the starter. If I recall from my Physics (before many of you were born) I think that Volts=Watts/Amps. As you increase the Amps being pulled, the Voltage decreases. After the car is started, the alternator starts to provide energy to the system in the form of Watts (power) and since the Amps (current flow) has stabalized, the Volts increase.

A Voltmeter is handy because it can give you information as to the general health of your electrical system. If you put a huge sub-amp in your car that draws a lot of current (Amperage), then your alternator may not be able to provide enough power (Watts) to keep your battery charged up. In this case you may see the voltmeter reading 10v while you are driving. Eventually, you will have a dead battery or a burned out alternator. Likewise, if you see voltages of 16v while driving, your alternator may be overcharging the system causing problems to both your battery and your electrical components. Finally, if you turn the key on with no accessories, and see much less than 12v, then your battery could be failing.

I'll be happy to have those that actually understand this stuff to chime in and correct anything I've screwed up.

dsmZ

iTrader: (5)

8v=replace battery. 10.5v minimum to crank the car. 12v is normal and 14.5v while running

beetlejuice

iTrader: (1)

I'm not an expert in 12v systems. But let me share this.

About a month ago, my battery was almost dead...car would barely start.

However, my voltmeter gauge was still reading ~12-14 volts.

Replaced battery...car started immediately. Voltmeter still reads ~12-14 volts.

Do not rely on voltmeter to gauge your battery's condition.

DavesZ#3

iTrader: (26)

When your engine is running, the Voltmeter reads the voltage output from the alternator, not the voltage generated by the battery.

If you stop the engine and turn the ignition on, then you're reading the voltage from the battery. If you're not reading over 12 volts, then you have one or more dead or dying cells in the battery.

Your battery may read 12+ volts and still not be able to start the car. It take current not volts to start it, if you don't have the power (current) then it won't turn over.