When I tried to start my car it did nothing I jumped it and it started I drove it for about 20 min. Got home and the check charging system mess. Came on I turned off the car and tried to restart it and it was dead air again. Next mess. In battery Save Mode. Charged the battery for 2 hrs. Battery didn't recharge and stated alternator Was bad. What else can I ck. Before having to replace the alter.
Measure the battery voltage with a digital voltmeter, engine off. It should be 12.6 volts if it's fully-charged. Measure it again with the engine running. It must be between 13.75 and 14.75 volts. If it is low, double-check the voltage on the large output terminal on the back of the generator. Whatever you find at the battery, you should find at the generator.
GM has had a really huge problem with their generators since the '87 model year. It's not uncommon to go through four to six in the life of the car. To reduce the number of repeat failures, replace the battery at the same time unless it is less than about two years old.