What should truck voltage be at?
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Sounds more like the battery is going bad.
14v while running is about right. 9v at rest is low.
load test the battery, 9 v at rest is too low
M.: First, you wrote
First, you wrote: "my battery light has turned on and off for months without issue" This means that you are unwilling to ACT when you are given NOTICE!! My understanding of this situation, is that you had an INTERMITTENT problem with your charging system. Next, you wrote: "around 9v but when started and driving jumps up a little above 14v" A properly operating charging system holds the system voltage to approximately 14.4 volts, if it can. A fully charged battery will show the charging system voltage when the engine is shut off and charging stops. Then the surface charge will slowly bleed off, until the battery voltage is approximately 12.6 volts. If the battery is discharged, the voltage can be less than 12.6 volts, but it shouldn't be less than 12.0 volts (approximately). What you're saying is that your battery is being discharged while the engine is off, OR is not holding its charge because the battery is injured. Injury can come from normal aging.
It sounds like the alternator is supplying the correct voltage but the BATTERY isn't holding the charge.
No. It sounds like a healthy alternator. 14 volts is good. Usually 13.9. If you get over 14.5 start thinking over charge. 15-16 you are frying the battery.
Go to an auto parts store and they will test the battery and alternator for free.
You have a nearly dead battery.
duck you sucker!
Was it 12 or 9? Was it 12v when key on; Then 9 on crank This is a Bit low. Some vehicles s will not turn on their electronic ignitions and/or ECM without 12.6 at crank. 9 on ignition too low. Either case, get a load test. Better safe than sorry. Check specific gravity, if too low in freezing weather even a brand new battery can split its cases
A fully charged "12 volt" system will actually run about 13.5 to 14 volts. If your system is only showing 9 volts before starting, then you have a weak battery. Get your charging system checked by a REAL mechanic. NOT some stupid auto parts store clerk.