We've got a 1999 F350 Diesel, the batteries keep going dead after about 4 days. We have checked for a draw-no draw.We have replaced the batteries 4 times-the last time with Ford batteries, we have replaced the glow plug relay. Any ideas?

 

If you've done it correctly, and you're dead certain that there's no draw, then there's only one other thing I can think of that would cause batteries to go dead in 4 days.... no charge.

First, key on but engine not running..... is the little red "idiot light" with the battery symbol lit? (We're checking the bulb here). If you have a light, start the engine..... it should go out. If it goes out, that would indicate that it's charging, but I'd put a DVM on the batteries to be sure. Should be about 13.8 V until the glow plug relay drops out.... then, it should be close to 14.5 V. If the voltage isn't up there, then the alternator isn't working properly.

 

We have checked all of this. It seems to happen with key off position, and everything turned off

 

This is dumb but...maybe your alternator is running 100% - so the batteries dont die in a day, but slowly lose charge over time? just a possibility i guess. Also - one time in my grandmas caddy (91) the blower motor was stuck on due to a relay. check your relays and fuses.

 

I would have looked at other things than batteries on the first set of new dead batteries.
Have you checked the voltage at the batteries, key on engine running?
Alternator wave form correct?