Little more information. When I left yesterday from trying to start the trailblazer my brother said his voltmeter showed 11.0 volts on the battery. A couple hours later is when it started with a jump. I drove it about 7 miles to autozone to get the battery tested. I shut it off. They hooked the battery tester on it at autozone. He said the battery shows its good, and reads 12.8 volts. We tried to start the car back up, and it did nothing. We tried to jump it, and still nothing. I finally gave up, and came home. Thats when I asked the question. This morning when I went back to start diagnosing it. It fired right up first time. I drove it about 10 miles back to my house. I never thought to check the volts of the battery when I got home. I just put the charger on it. I set it on 2 amp charge, and when the charge meter came on it said 50% charge. So it usually takes a couple hours to charge a 12 volt battery when it reads 50% charge on my battery charger. I came back inside, and 20-30 minutes later it was reading 95% charge. I let it sit for another 30 minutes and it never changed. I thought it was strange it charged from 50-95 so fast then stayed there. I unhooked the battery charger, and tested the battery. It showed 12.50-12.80. It bounced around a lot, but kinda settled around 12.7. I started the car while the voltmeter was attached to see if the volts dropped real low. It went down to around 11 vols while it started. Then it went up to about 14.8 when the alternator was charging. So is it possible the battery was just weak? It cranks and fires up everytime now. I don't know what else to test. I can't really find a problem til it happens again. Any thoughts?