What year, engine, and miles?
My Jeep runs at about 14 volts also, and is fine.
1st thing, have your battery checked. A bad battery can cause the issue you are having.
Next, check the alternator output. (Both of these can be done at your local auto parts store, usually for free)
Last, and this is what gets some people, is corrosion inside your positive battery cable. This can reduce the flow of electricity and cause the issues you're seeing. Just cut and peel the insulation back about 3-4" and if you see any deposits, replace the cable.
Let us know what you find after checking these.