Need help!!!!1988 c1500 5.7 rwd.

[ShortBoxSheezy]

Tried Starting my truck today got a slow crank no start tested my battery had over 12v cranked it a few times still no start but as I was trying to start it slowly got weaker so I checked the battery again and it was drained?

 

[HotWheelsBurban]

Check your connections at battery, grounds and starter. If there's corrosion anywhere that you can see, there's probably more that you can't see.

 

[Schurkey]

Tried Starting my truck today got a slow crank no start tested my battery had over 12v cranked it a few times still no start but as I was trying to start it slowly got weaker so I checked the battery again and it was drained?

Punctuation and sentence structure matter.

How much "over 12v"? 12.6--12.7 is fully-charged. 12.2 is half-dead. How old is the battery? Can you see if the electrolyte level is low?

Poor connections, failing alternator, excess starter draw are all possibilities. More diagnosis needed.

Clean and inspect the battery cables, fully-charge the battery, see if it starts. If it does, you can check charging voltage at the alternator, and at the battery. Battery capacity, parasitic drain, starter draw, alternator amperage output will be more difficult.

 

[ShortBoxSheezy]

The battery is new, after a few cranks it’s draining tho. Even when I’m connected via jumpers to my other vehicle it tries then slowly dies out, still no start. I can hear my fuel pump when I turn the key, and I’ve cleaned my connectors. Im stuck not sure what’s going on. I had the truck stored for a year, now this. Moving on to the alternator.

 

[Schurkey]

FULLY CHARGE the battery, then have the battery tested. Preferably using a REAL tester with heavy cables, that loads the battery. Not a hand-held job with light/small cables that measures capacitance, or resistance, or plays Van Halen at the battery until it submits.

Yes, the alternator is suspect, as are all the cables/wires until proven otherwise.

What is the starter amperage draw? I've seen the draw so high (over 500 amps!) the cables turn into electromagnets and snap up against the sheet-steel fenders.

Is there a parasitic drain on the battery?