bad batteries or something else.

[2008chevy2500]

i have a 2008 chevy 3500hd 6.6 last winter 2014/2015 I had to replace glow plugs so I did. Before they started going out I started having problems with the truck loosing all power after the glow plugs cycled and I would have to turn the key off and then start the truck. most cold nights I kept it plugged in(Virginia) not too cold and it would start no problems as it wouldn't use the glow plugs. after the summer months it has started back again. i have had the batteries tested and they both read good the cca on the batteries are 770. one battery is reading 719cca and the other is reading 728cca. is it the batteries causing this or is it another problem? thanks

 

[NC-smokinlmm]

You disconnecting them when you load test?

 

[Al's max]

Are you driving the truck everyday or does it set for a couple days without driving any?

 

[Big Block 88]

How does the starter sound when it is spinning?

 

[danzick]

already posted this once, but maybe it didn't go through. check the glow plug relay.

 

[2008chevy2500]

Yes i have unplugged the batteries when load tested and i drive it every day it does it on cold starts and the starter sounds fine