I too have a PC680 and as stated above, it only gets the charger if

1.) I flip the master on and see < 12 volts

2.) have the avionics on for an extended period

It goes against what Odyssey says, but I've only heard of the PC680 dying young when constantly on a trickle charger.

It's hard to believe you have had that much trouble with your Odyssey batteries. I am on my third one in 10 years. I generally replace every 3 years or so just because. All of our RV's in my area are also running Odyssey batts, I haven't heard of anyone having trouble either. You need to look at the possibility of other problems. First, not knowing how old your kit is and not knowing when you purchased a wiring kit, you need to see if you have the bad cables that were delivered a few (4 or 5) years back. Van's (or their vendor) used the wrong die and under-crimped the #2 gauge wires in many wiring kits. I helped a friend build a '7A. All was well until a starting problem developed after a few years and was traced to under-crimped wires. He had also replaced his battery thinking that was the problem. After cutting of the nice heat shrink tubing you could clearly see the wire move inside the terminal end as the crimp was not deep enough. You need to perform a voltage drop test of your starting system. It's easy to perform if you know how to do it. You can look it up on google or contact me and we can go over how to do it. I simply cannot believe you have had such poor service with your batts.
Rex 530-945-9000

680
 

I am on my second Odyssey over 6 years but the first one is still starting my lawn tractor on a regular basis. I don't use a maintainer and even if the airplane sits for 2 or 3 weeks, the battery cranks just fine.... no issues. I will buy another when the time comes.