Jump started with cables on wrong posts

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14RamMan

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I jump started a friend’s truck last week, but he had the cables on his battery backwards (even after me reminding him to check). The connection was made for about 3 seconds before we stopped and realized what was done. 3 days later I woke up to a dead battery after driving it the days prior. I figured since it was 2.5 years old and had been incorrectly jumped, it was dead. I got another battery and all was well until this morning when the new battery was dead (another 3 days later). 2 hours on a battery charger and it was good to go.

My battery is charging while the truck is on (approx. 14v while running), but slowly loses a charge when off. No trouble codes. My best guess is a diode in the alternator went bad. Anyone else have any suggestions on what it could be?
 

Racer_X

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Agreed. Bad diode.

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chopperman1

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Easy enough to prove. Disconnect the wire from the alternator and put a amp meter in line, will tell you if the alternator is drawing any power.
 

O.R.T.

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Easy enough to prove. Disconnect the wire from the alternator and put a amp meter in line, will tell you if the alternator is drawing any power.

^that^ BUT DON'T DO IT W THE HOT TO BATTERY LEAD OR YOU'LL COOK SOMETHING ELSE IF YOU SHORT TO GROUND ON ACCIDENT.
 
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14RamMan

14RamMan

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Im going to take it in to a good shop near my job and let them do some diagnostics. Ill report back on the findings.
 

chopperman1

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Measure the current flow on the battery's negative lead, much safer method.

That's just going to tell you that something is drawing which we already know is due to a dead battery in the morning. To isolate the component that is drawing it you need to go to that specific piece, in this case the suspected alternator.
 

huntergreen

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had that happen back in the seventies. needed a new battery and alt.
 
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14RamMan

14RamMan

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they had it all day and werent able to find anything.
 
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14RamMan

14RamMan

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Woke up and it was at 9.5V. Not enough to start up. I wonder if I should just change the alternator out myself and see what happens.
 

Sir John

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I'm no expert, but there's not a whole lot it can be based on your story above. Very surprised your shop wasn't able to figure it out. ****, i bet Advanced Auto could quickly tell you if it's a bad alternator. I would have to agree with most....bad alternator, but they aren't cheap. Try to make sure before you buy one.
 
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14RamMan

14RamMan

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I replaced the alternator last night, and same thing this morning...dead battery. I'm going to swing by Lowes this morning and grab a multimeter capable of measuring DC currento and systematically pull fuses until I find the circuit. I installed a different head unit (pioneer avic 8200nex) last week and wonder if it's causing a drain. I've checked the wiring multiple times and it's correct.
 
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14RamMan

14RamMan

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Update: It looks like about 1 amp is drawn when the truck is turned off for about 5 mins, then .04 amps remain drawn (within the range of normal). I purchased a new battery thinking the old alternator messed it up. SO i now have a new alternator (installed last night) and a second new batter (Duracell AGM installed this afternoon). As soon as I turned my truck off, i measured the voltage at the terminals; it was just about 13v which makes sense since it was just turned off. 2 hours later, its reading 12.44v...is this a bad thing? what else could it be?
 

pcschwenke

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I would pull one fuse at a time to see what's draining the power. Maybe check the radio one first.
 

dkmesa

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sorry for your trouble. this is why i've never allowed someone else to connect jumper cables if my car is involved.
 

SilverRam11

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How's the other truck? Sounds like you both connected power terminals to ground, shorting both batteries. With the batteries installed in the trucks, you could have shorted everything hooked up to your battery. It's not necessarily the end of the world, but it sounds like you fried something. Start with fuses. I was turning a nut on a battery terminal once and hit the other terminal with the wrench, that was a pretty blue spark and welded the side of the wrench a little.
 

adrianp89

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A new battery should sit over 12.6v. .04 is 40 mA and is high. Not high enough to kill a battery over night though.
 

kayakersteve

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My kind of mechanic - Replace stuff until the problem is fixed!
 
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