Thanks for answering! I'm sure the battery is good as it's only 4 months old.
I'll have my mechanic check this out the next time I go for service...unless it
gets worse in the mean time! ;-)
If you could (or not) verify that problem with a good hand-held voltmeter,
then I could say that the car's gauge is either good or bad. If there is
an electric lighter for cigarettes available, that socket would be a
convenient place to monitor the car's voltage. Have a passenger watch
this, while you drive, or let somebody else drive while you watch the
Saving the worst for last:
If the voltage is steady on the hand-held meter, but the car's gauge still
jumps, the gauge may be poorly grounded, badly connected, or otherwise
faulty. There are generic aftermarket digital gauges available, if the old
gauge is dying, and a replacement is not reasonable in cost. A good
salvage yard (or Internet) might help you, there.
If the voltage fluctuations are real, then un-bolt and clean *each*
each battery wire, + & -. Dirt is an insulator. Find and check the
fusible link from the battery to the alternator, if your car has one. If
bending the fusible link slightly changes anything, it is bad. If the
battery cables -look- bad, then they probably are bad. Check that the
alternator drive belt is not worn, damaged, or loose. Check that the
alternator wiring connections are clean and bright, both male and female.
Corrosion stops electricity in erratic ways.
Have the battery checked, by an auto-parts store that sells a battery
brand that you like. Your old battery may have some warranty left on it,
too. Cells may be deteriorating, and good weather never lasts.
If the problem persists, and the gauge, cables and battery are good, then
the problem will probably be caused by the voltage regulator in the
alternator. This is replaced as a unit with the alternator.
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