What would cause the battery in your 1986 Chevrolet to keep dying?

Simple things first. You may have a bad battery. You may also have a bad battery cable or cable connection. You may have a bad voltage regulator in your alternator. To check the voltage regulator sit behind the wheel and turn the key on. When the warning lights appear does the battery light come on? If it doesn't light up it means the voltage regulator is not completeing the circuit.

Now if you have checked all of that and are still having problem, you have an electric vampire somewhere in the car. Could be a shorted wire or a courtesy light that is staying on like under the hood or in the trunk. When you drive the car at night do the headlights seem to dim off and on? if they do you have a ground wire problem

Good luck