I know there have been a couple posts on this topic, as I found doing research however, I thought I would share the solution I found as there has not been an update on the topic in a couple years and I know more and more HDJ81s are filtering into the US.
For those who aren't familiar (and as I have come to find out) with the 24V/12V dual battery system on the 81, the truck uses dual 12V batteries wired in parallel when running. The exception being that these batteries operate in series during the start up in order to operate the 24V starter however, once started a relay opens and the truck operates everything normally again as 12V in parallel. With the hood open and standing in front, the battery on the left is the starter battery. The battery on the right with the big plastic cover and warnings all over it is your accessories battery. If you need to jump start, only connect to the starter battery and not the accessory battery (bad things will happen).
Problem: Went to start the 81 the other morning (32 deg) and I got a rapid succession of clicks with no turn over. Checked the battery for electrolyte (full) and with a multimeter (12.27V). Since the batteries are paralleled, I waited to see if the starter battery voltage would change and it did, going back up to 12.41V. This led me to believe that the starter battery was bad and drawing off of the accessory battery. After some research on MUD I found the battery sizes to be a Group 27 and Group 27F (reversed positive terminal).
Solution: Knowing that an old battery in a parallel system can leach a new one I opted to replace both batteries. Shopped among all of my local suppliers and found I had 2 options. 1). Optima (Johnson Controls) yellow/red top at $298ea. 2). Superstart (East Penn/Deka) at $129ea. After a bit of research I discovered mixed reviews on the Optima's stating they aren't what they used to be and they typically last 3-4 years and have a 36M warranty. Likewise the Superstart typically lasted around 4 years with a 24M warranty. After some careful consideration, it appears both batteries have the same life span with one having an extra 12M of warranty. The question being, is that additional 12 months of warranty worth the $338 additional dollars? Short answer: F-No.
So here is what I went with:
Starter Battery: Superstart 27, Part #27PRMJ, CCA 810, 140 minute reserve capacity.
Accessories Battery: Superstart 27F, Part #27RPRMJ, CCA 710, 165 minute reserve capacity.
Purchased both batteries from O'Reilly's (because they were in stock) and installed them into the 81 and it started up like a champ!
I understand some people have done the conversion to a 12V system and that may be in the future someday but for now this worked. If anyone has a write up for the 12V conversion with part numbers or additional insight, that would be awesome.
For those who aren't familiar (and as I have come to find out) with the 24V/12V dual battery system on the 81, the truck uses dual 12V batteries wired in parallel when running. The exception being that these batteries operate in series during the start up in order to operate the 24V starter however, once started a relay opens and the truck operates everything normally again as 12V in parallel. With the hood open and standing in front, the battery on the left is the starter battery. The battery on the right with the big plastic cover and warnings all over it is your accessories battery. If you need to jump start, only connect to the starter battery and not the accessory battery (bad things will happen).
Problem: Went to start the 81 the other morning (32 deg) and I got a rapid succession of clicks with no turn over. Checked the battery for electrolyte (full) and with a multimeter (12.27V). Since the batteries are paralleled, I waited to see if the starter battery voltage would change and it did, going back up to 12.41V. This led me to believe that the starter battery was bad and drawing off of the accessory battery. After some research on MUD I found the battery sizes to be a Group 27 and Group 27F (reversed positive terminal).
Solution: Knowing that an old battery in a parallel system can leach a new one I opted to replace both batteries. Shopped among all of my local suppliers and found I had 2 options. 1). Optima (Johnson Controls) yellow/red top at $298ea. 2). Superstart (East Penn/Deka) at $129ea. After a bit of research I discovered mixed reviews on the Optima's stating they aren't what they used to be and they typically last 3-4 years and have a 36M warranty. Likewise the Superstart typically lasted around 4 years with a 24M warranty. After some careful consideration, it appears both batteries have the same life span with one having an extra 12M of warranty. The question being, is that additional 12 months of warranty worth the $338 additional dollars? Short answer: F-No.
So here is what I went with:
Starter Battery: Superstart 27, Part #27PRMJ, CCA 810, 140 minute reserve capacity.
Accessories Battery: Superstart 27F, Part #27RPRMJ, CCA 710, 165 minute reserve capacity.
Purchased both batteries from O'Reilly's (because they were in stock) and installed them into the 81 and it started up like a champ!
I understand some people have done the conversion to a 12V system and that may be in the future someday but for now this worked. If anyone has a write up for the 12V conversion with part numbers or additional insight, that would be awesome.