Low voltage

[Junglekat90]

I have a 4.7L obd2 swapped into my 1990 yj that had a 4.2L. Since the swap i have noticed that the volt meter is running around 10-11v while running and drops down to 9-10v when I have the headlights on. This has been causing rough idle when Im stopped at a light. Ive read some places that it could be a bad battery. The battery should be ok but it is something I need to check out. Im wondering if there is anything else that may be causing the problem.

[SilverXJ]

Have you checked the voltage with a meter?

If that is the true voltage I would look at the alternator.

[Junglekat90]

battery reads 13v while running and alternator also reads 13v. the gauge was reading below 10v.