I have searched and got 202 pages of results with nothing specific to the actual numbers one would expect to see for battery load testing. I know I will need a load tester and disconnect both batteries to figure out which is bad. I'm wondering what I should expect to see for numbers on good batteries.

My current numbers are, 12.79, 11.74 and dropping slowly wait to start. 7.5 on crank. On a gasser it should not drop below 12 on crank indicating a bad battery if it does, is this the same for a Diesel?

 

You need 10 volts to start.

 

It starts on 7. Just wondering what it should be

 

If you are saying that it drops to 7.0 with the starter engaged, I would think that was close to accurate.

 

Typically the PCM won't fire the injectors unless it sees about 10.5 volts but that isn't a hard rule. Each truck is different. Battery condition, glow plug operation, starter draw, ambient temp all have some effect. While cranking, I rarely see the volts dip into the 10v range...most times it cranks around the 11.2-11.7 range. If I see the volts drop into the 10s while cranking then I usually check my battery connections for corrosion. If I see the volts dip into the 9s then I usually have about 6-8 weeks before it's time to get a new pair. My truck eats batteries every 2 years, almost like clockwork.

Here are readings from one of my trucks....

Hope this helps.

 

That's what i'm saying 7 volts while cranking (starter turning motor). I'm wondering if that's normal. It seems really low to me and i'm wondering if its normal or if I should start testing my batteries and replace?

 

I went out and started my truck.
50 deg. 1st start today. 12.5 volts with a Power Point Plug in Volt meter.
Key on and drops to 11.2, and with starter engaged dropped to 9.8volts.

Now I don't have a lot of faith in the accuracy of this tool, but they are usually close.

You might go by the parts supply store and have them check each battery individually.


Evidently I type too slow.

 

Thanks, Yeah I probably will and should get them checked not sure how old they are they were in the truck when I bought it.

 

7 volts while cranking is dangerously low. You are flirting with a no start condition pretty soon. The PCM shuts down when voltage falls below 7 so it's amazing that your truck even starts. Possible bad batteries or bad starter is my guess. For me, bad batteries are more common. I've never had a starter go out on one of these trucks yet (although I am sure my number will come up one of these days...)

 

i just put in new interstates and checked at a battery.11.8 gp's on and 10.9 cranking.i had my old set load tested by my mechanic.now he has a tester also but u can do it at home on your own.
1.he said let bot batteries hooked up and put a voltmeter on one.take the reading.let the meter on and hooked up.turn key to on and turn on lights stereo and turn your blower motor on high.there should be a slow drop.if after 4 minutes they really fell off to 8-9 volts they are shot.

 

voltage could show lower than normal if you start cranking while gp are still glowing.

 

I waited for the light to go off but I was under the impression they stayed on for 180 seconds regardless?

 

gp usually do stay on longer than the light , mine do anyway

 

my gp'are on when cranking at that 10.9

 

I just had to replace my batteries. I have AZ gold tops in it. I had them put in at the mechanics in June 2010, and worked great till June 2011, one was bad and the other was low and on it's way out. The warrantied them then, it lasted till this week, I had to have them replaced because of the same problems again. It seems it is always the main battery that goes bad first, and the one on the drivers side that goes second, or at least that is what I have noticed for the past 3 years with this truck. They warrantied them out again, I guess I am good for another year.

If they go bad again I am either going to go pick up some Costco Interstate Batteries, or more likely some Bosch ones from Pepboy's as they have a great warranty prorata program, in that the warranty starts over with the new ones. Not from the original date of purchase like everyone else.