Odyssey did come back with an answer on what they thought the reason was that I killed these 2 batteries so quickly.
They claimed the problem was sulfation of the battery by being stored (even shortly since I fly almost once a week) at something less than full charge.
Apparently the Odyssey is can sulfate quicker than other types of batteries due to how it is made and how thin the plates are.
Symptoms of this failure mode are apparent full charge voltage but no capacity to do any real work....
They claimed that the issue may have been my constant use of the Odyssey Ultimizer Charger (almost any smart charger will have the same issue).
They said that the Odyssey battery needs to spend a certain amount of time in the absorption phase of the charge. The length of time spent here is dependant on how discharged the battery is. The voltage needs to be at least 14 or more volts during this time. The manuals say 14.7v.
Here is the theory...When using the Odyssey Ultimizer, the charger looks at the voltage of the battery when you turn it on. If the voltage is high enough to start with or rises quickly, the charger will very quickly kick into trickle mode and won't spend much time in the absorption phase of the charge. Odyssey says this can cause what I experienced due to the fact that the battery is not getting fully charged.
Their recommendation was to always discharge the battery enough that the Ultimizer charger will not think the battery is fully charged quickly after hooking it up and turning it on. This will allow the normal absorption charge cycle to complete properly.
So to recap here are their recommendations:
- Never store your Odyssey battery (even for just a week, the effect is cumulative) on less than a full charge
- Never put the battery on the Ultimizer charger unless it is discharged enough to allow the absorption phase to complete properly. If it quickly switches to trickle after you used the battery, most likely it will not be fully recharged.
I think my habits of doing a ton of avionics tweaking/hangar flying on the ground and constantly just trusting the Ultimizer charger to take care of the battery was what killed my two batteries prematurely. I remember it switching to trickle quickly most times.
Folks that fly often and always fly long enough to allow their alternator to recharge their battery fully after starting may not experience this issue often if ever as long as their main bus volts are up where they need to be.
Folks that have low main bus volts while the alternator is running may have issues prematurely. The manual wants 14.7v...I doubt many of us have that high of main bus voltage while running. Mine runs between 14.2-14.4 and I have an internally regulated PlanePower alternator.
Since learning this info, I always either fly long enough to allow a full recharge or if I use the Ultimizer charger, I always run some load until the surface charge of the battery is burned off. This allows the Ultimizer to spend all the time it needs in the absorption phase. The difference in the time it takes to switch to trickle is significant using this method. So far so good with the replacement battery!