What could've caused my battery light to come on and then my car to overheat?

What is your question?

Drove fine to work, went out for lunch noticed battery light first and then all of a sudden my temperature gauge went into the red zone and a red light came on. Checked the coolant, it was low. so I added some coolant and car seemed happy for the few minutes the warning lights went off. Then back on they went. I pulled over and had it towed... I have replaced the reservoir tank already, so it shouldn't be a radiator issue. I just most recently had some ca-smog things replaced. Wondering how much money to fix this time and/or is it time to give up?