No, your alternator may not be charging. It should go up to about 14 volts. However, if you have an afterglow-glowplug relay, it will stay around 12 volts for 2-4 mins. To make sure thats not the case, start the car and let it run like 5-6 mins and then check it. If its back up to 14 volts or so (or close) then that means you have afterglow that uses a lot of power the first few mins after startup.

I think even with afterglow on revving it to 2500 should have shown a difference on your meter. I'd do the above check first though.

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