As suggested above, remove the battery cables, clean them and the posts, and measure the battery while disconnected. It should be just over 12 volts. If not, hook up the battery charger.
With a charged battery, and the car running, check the alternator light.
If you can find a local alternator-starter repair shop, have the old one rebuilt. Rebuild shops are hard to find, like radiator repair shops, and engine machine shops, they are fading away. A new Valeo alternator is plug and play. It is a real challenge getting the wires hooked up with the air diverter in the way.
I had my tachometer modified and got rid of the dumb shift light, and had a volt meter added. It sure is comforting to see the alternator charging when driving.