What is draining my battery?

1998 OLDSMOBILE BRAVADA
177,000 MILES • V8 • 4WD • AUTOMATIC
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LARRY KELTY
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The vehicle battery is at full charge. As soon as I hook up the positive cable it goes from 12.7 volts down to 4.5 volts, I take the positive cable back off and the battery voltage starts going back up. The vehicle will only try to start if I have my battery charger on it and switch it to 200 cranking amps and spraying starter fluid however the vehicle never does start, I believe the entire system is being drained and will not allow it to receive any spark whatsoever without the battery charger it will not even turn over. however, it is not blowing any fuses or relays it I can tell and there's no smoking wires or anything like that I can't tell what this could be. thank you I appreciate any help I can get.
Sep 26, 2022 at 9:50 PM
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STRAILER
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Yep, it sounds like the battery is no good, I would get a new one and install it. Here is a generic guide that can help with instructions in the diagrams below to help with your car:

https://www.2carpros.com/articles/how-to-replace-a-car-battery

Check out the images (below). Please let us know if you need anything else to get the problem fixed.
Sep 27, 2022 at 10:44 AM
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LARRY KELTY
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I have replaced the battery with a new one. The same thing happens unhooked alternator hooked positive cable back up battery goes drains immediately with or without key on and will not turn over. I will only have ignition and dash light and it will only turn over if I have 200 cranking amp battery charger hooked up but still will not start.
Sep 27, 2022 at 6:15 PM
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STRAILER
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Is there a large spark when you connect the battery? Can you upload a short video of the battery connection? If there is not a large spark, then the battery has gone bad/defective. Can you turn the headlights on and are they bright when you crank the engine over?
Sep 29, 2022 at 12:56 PM