1999 Mercury Cougar Any suggestions on what electrical area

My car is a 99 mercury cougar.

The problem is, I start my car and it starts fine, I let it sit there to warm up. While its running the gas and other gauges magically all die and go to empty, etc. So I turn my car off and attempt to restart it to see what it does and it does a clicking/brushing kind of sound. If I let it sit for awhile it will start but the guages do the same thing after a bit. I already know I need to get the starter looked at because of previous problems but with the gauges screwing around like that do you think its more of a battery on the verge of totally dying or a bigger electrical problem. The radio and headlights all work fine, but it takes more juice to turn the car over and such im not real car saavy so im lost. Just trying to get a general idea of what the problem could be before I take it in to see a mechanic if that.