Thanks Tom. I am going to try it!

 

I replaced both batteries with recommended Interstate batteries about 2 years ago. I noticed in the last few months it seemed to turn over slower. Had to let it sit about a week and went to start and the wipers "wiped" and nothing happened when I turned the key. Set it up on a charger overnight and started it the next day and went on my way. It went a week again without being driven, and I had the same no start result. Out of curiosity I popped the tops off the batteries. All the cells on the passenger side battery were dry, and half of the driver side cells were dry! I topped both batteries off with acid, charged for three days and it started like a champ. But...again, after a week...no start. I haven't dug into it any further, just wanted to suggest you pop the tops and see if you might be battling dry cells in your batteries.

 

Batteries are topped off with distilled water, not acid.

10.5 volts usually means a shorted/reversed cell. Battery is done.

 

Ohhh shizzzz... still I wonder why they went dry.

 

FYI leaving a lead acid starting battery or battery bank on a trickle charger for extended periods without a substantial load every so often allows dendrites to grow between the plates and will eventually short them out. It is known as "mossing" in the battery world. I wondered why my batteries were shorting out after a couple years even though I was using a Battery Tender on them, then I got interested in de-sulfating and did a lot of research. Dendrites begin to grow on every battery during charging, but the relatively high amp draw of the starter motor load knocks them off. It is recommended that a starting load be applied every couple days during trickle charging to keep the dendrites in check. This is why batteries installed in vehicles that are used daily last the longest, provided the charging system is correct.
When de-sulfating a battery in the shop I now apply a load of at least 100 amps for 10 seconds every day or two with a carbon pile.
On my truck I have been using the Battery Tender very sparingly. I will park the truck on Sunday, then wait till Wednesday or Thursday and plug in the Tender knowing I will be starting it on Saturday. So far it seems to be working, my Motorcrafts are going on 5 years now.

 

Wow, I never heard of that. I have now two things to ponder. However, I have kept my Expedition on a smart charger for 6 years now and no problems yet. Same with my Tractor but only 2 years on that. But three shorted batteries on my truck in 8 years seems to indicate there is something like dendrites going on. Thanks for the info!

 

Sorry for not updating, I just got back from the States. I found my starting issue. The wiring harness inside the driver side valve cover was melted on the one end, affecting the number 4 glow plug. Replaced the gasket and harness and and the truck has been starting great. Thanks for all the suggestions.
George