I have a 7.3l diesel 2001 Excursion that won't retain enough power in the batteries to start. This started a few days ago. I replaced the positive cable about 6 months ago. I've had the batteries, and alternator checked and they're all fine. One bolt on one of the negative cables clamp was bad so I replaced it cuz I wasn't getting a solid connection to the battery post. I've had to get jumped to get it started and it runs great..it just won't hold enough power to turn it over. Is there a short somewhere or is something draining my batteries??? Please help.

 

Get yourself a voltmeter and check the batteries and the connections. To check the connections, put the black lead of the voltmeter to the neg. post of the battery. Put the red lead to the wire, not the post of the positive. You should get the same reading if you put the red on the positive battery post.

Do the same for the negative on both batteries. Did you clean the posts and clamp?

When they checked the batteries, what was the voltage?

 

are your glow plugs working properly. I was having same issue. I replaced the batteries with delco ac and replaced glow plugs and ebpv as well as it was beat. No more issues. Also when you go to crank will it crank or just click and nothing. If it cranks do you see you meter dropp to around 10ish?

 

When they checked my batteries I do not remember what the voltage was. I put a voltmeter on them today, despite the fact that they're almost dead, and 1 battery gave me a reading of 26 which stayed the same regardless of where I touched the lead wires to. The other battery varied though, it was either 21 or 25 depending on if I was touching the cable or the battery post.
I had 4 glow plugs replaced maybe 1 1/2 yrs ago but that was a very different and noticeable problem than this. The battery cranks after its been charged a bit but then it just winds down until it clicks, clicks, clicks.
I also checked all the connections on the neg and posi cables today all the way down to the starter/solenoid and all was good.
And yes I have cleaned all the termiminals and posts and wiped away any corrosion on them. When I would start the truck the panel battery meter would drop low, maybe around 10. Also the meter would show around 12-14-ish when the key was turned on and it wouldn't jump up to the 18-20 range until after it was started/running for about 30 seconds

 

Could you clarify?