I’ve got an 88 Cutlass Supreme V8. It was sitting for a few years and I decided to start driving it again. I got a new battery and changed the oil and coolant. It fired right up and ran great. Now this was about 2 months ago. I haven’t drove it anywhere because I haven’t got it registered yet and I’m prepping it for paint. But for the past 2 months I’ve started it up everyday and let it run for 15-20 minutes with no issues at all. Then one day I had it running, turned it off, tried to start it a few hours later and nothing. No click, no lights (inside or outside), nothing what so ever. Battery tests 12.4 volts. If I disconect both battery cables then touch the cables together (completely discharging the car) then reconnect the battery, the dash lights will come on. But when I try to start it I lose all power again. The car will be completely dead until I disconnect the battery and touch cables again. What can cause this?

Not sure if it helps, but prior to the car sitting i didn’t have any issues with it. Drove it for 5+ years with no problems.

 

I will also add that early on you said your battery was only at 43 percent charge. After you drove the car for 30 minutes it still was not at full charge. At 43% charge you will need to drive the car for more than 30 minutes to recharge the battery to full charge. Probably more like 60 to 90 minutes and this also depends on your alternator output and the gauge of the wire in the charging system. If you want to dabble in this kind of stuff you should take a class on basic auto electrical. Never stop learning.