key off amp draw test

[brian89]

yea im pretty sure that i have a draw on my batteries when the truck is off, they go dead with the lights on at idle but runs fine with them off, if i shut it off the batteries go dead like nothing even after it has been running for a few hours, and if i unhook them they hold power a little better, but if i let them hooked up they dont hold power for ****, when running with nothing on they carry 12.3 volts, i just put batteries in it but they were slightly used, i am trying to figure out how to do an amp draw test with the key off, i know on a motorcycle you do this at the main fuse but im pretty sure my truck does not have just one fuse that i could test this at, so if anybody has any good ideas on how to test this it would be very much appreciated

 

[907DAVE]

Amp meter in line with your main cable and battery, leave the other battery disconnected.

Acceptable reading is .050 amps or less. If it is high wait 1 hour (amp meter still in line) to let all the modules "time out" and recheck. Be sure not to disturb the truck during this period as you can wake up the modules by simply opening the door.

 

[brian89]

Thats the red cable correct? And which battery? Passenger or driver side?

 

[907DAVE]

On yours it will be on the passenger side. You can do either positive or negative, as long as there is no other place for current to flow, as in an additional power or ground for an accessory, etc.

 

[JLDickmon]

when running with nothing on they carry 12.3 volts,

You have a battery with a shorted cell, or an alternator with a grounded diode.

 

[brian89]

i tested the output on the alternator last night and it was only putting out 12.6 volts at idle and the batteries were only getting 12.3 at idle, so im guessing that the alternator is all but shot, and could running bad batteries for an extended period of time, like 15.5 hours straight, make the alternators weak or bad?

 

[brian89]

and will running bad alternators make the batteries go bad more quickly?

 

[907DAVE]

Ohh yeah, how else will they stay charged?

 

[brian89]

well went and bought a new top alternator for $200 and it runs and charges better now, at idle batteries are getting 13.6v, still a tad low i know but it is better than it was, gotta save $200 again for new bottom alternator, thanks for your help guys, much appreciated