Been having a slow cranking problem after parking the truck for a few days. Its the batteries. So i charged them up, but the problem returned. Now I have been monitoring the battery voltage decaying over time. 24 hours after charging, they are sitting at ~12.7volts.

The simple question, who's answer I have never seen strangely: What is the minimum tolerable voltage for our batteries (2003)? What is the range of voltage for a good batt? I don't have the capacity to load test them, so i'm just checking voltage for now.

 

Good question, I am just subscribing to the thread

 

The minimum voltage usually comes when cranking and with the glow plugs on. Remember, the glow plugs can stay on for up to a few minutes. This is when the FICM is really put to the test. I put a DVOM on the batteries and had someone crank. The voltage dropped quite a bit lower than the voltage I read at the powerpoint plug (have a gauge) or the DashDaq.

A recent TSB states that the minimum KOEO voltage is 11.5 - IIRC.

 

TSB 10-12-6
6.0L - RUNS ROUGH, LACKS POWER, HARD START, NO START

The FICM contains two major internal components, the main circuit board and a DC-DC converter. The DC-DC converter is the device that amplifies battery voltage to 48 volts to operate the injectors.

Low FICM supply voltage results in increased FICM operating loads, potentially damaging or shortening the life of the FICM.

For contribution codes without circuit codes, go to Powertrain Controls/Emissions Diagnosis (PC/ED) pinpoint test P. Do not continue with this procedure.

Connect Integrated Diagnostic System (IDS) scan tool and confirm battery voltage is greater then 11.5 volts key on engine off (KOEO).
If battery voltage is less then 11.5 volts KOEO, do not continue with this article. Refer to Workshop Manual (WSM), Section 414-00.
If battery voltage is 11.5 volts KOEO or higher, continue to Step 2.
Remove the FICM relay.

 

Also, I don't believe you will get it to start w/ a voltage less then 9.5V.

 

Thank you once again Bismic. What should we do if KOEO voltage is below 11.5 volts? New Batts? I've heard the voltage draw while cranking is an important number. Whats the minimum cranking voltage before the batts are bad?

 

So here's what i got.

Starting: 12.8
Cranking:10.6
Recovery:12.1
After Alt: 14.1

Is that cranking drop to severe??

 

That cranking drop is normal. There are a number of threads on this subject and multiple folks post drops to that range. My new batteries dropped instantaneously to 10.6V at its lowest point during cranking (actually 10.4V w/ lights and all the accessories on). IMO, if it drops to below 10V on cranking, then you may have an issue. Also, the voltage should drop and then recover VERY quickly.

 

Go to your local automotive battery outlet and have them load test the batteries separately. If one fails replace both.

 

That seems like an easy question but there isn't a straight answer. A new fully charged battery is designed to supply 2.25v per cell for a total of 13.5v. As a battery ages, voltage drops due to sulfate build up on the plates and in the bottom of the case. Other things can lower the reading too, like overheated plates that bow inside the case causing shorts, and cracks where the post(s) connect to the plates caused by heavy handed installers. Also the electrolyte can be contaminated by minerals which reduces voltage output. All (any) of these things reduce the capacity of the battery to store electricity but some of them don't reduce the voltage reading you migh see immediately after charging. Generally, shorts or opens anywhere in the system will reduce volts to a point a simple check with a voltmeter will tell you it's bad while the other issues may not reveal any problem. Putting a load on the battery and watching the volts may show you if there is a problem, so it is possible to watch voltage and flip on the headlights! you will not get a "number" this way because you need to include "time" in the math required to make to calculation of the batterys reserve capacity (health, expressed in amp/hours) but it is a valid way to do a "side of the road check". If the voltage drops quickly, say from 12.2 to 8.? in a count of 10 (after charging) you need a battery. If it drops slowly, say from 12.2 to 11.? in a 10 count it's got some life left in it. It is possible to see a battery with 13.5v (after charging) to drop to 5v pretty much immediately or see one at 13.5v that stay's above 13 for the 10 count.

I guess I'm trying to say it's a "feel" thing but it's possible to pick up on it pretty quick if you do it a few times. It's just not possible to determine a battery's health with just a voltmeter, only it's unloaded charge.


Here is a usable battery tester for twenty bucks:
Battery Load Tester - 100 Amp, 6v/12v

 

you should also be doing avoltage drop test on the battery cables and connections there should be amax .2v drop per cable preferable to have ov drop

 

+1 on the load tester. A tool that will pay for itself many times over in it's lifetime.