I'm just now replacing my 05 EG original battery..just called today to Batteries Plus..they've got an X2 made by Deka with a 2 yr warranty for $135...said they would give me $10 off that price since I was looking at batterymart online...already charged and ready to go...

 

Yep +2.
Plugged in all the time when at home in the garage, 24/7, 365.
An once of prevention...worth a pound of cure.

 

If you've got two batteries that have lasted a year or less there is some problem causing that.

Have the batteries ever been weak enough to not start the bike in those 9-12 months, or do they just simply fail at that time?

If the battery has been "down" during those 9-12 months of service, then BlackPearl#1 is probably correct and you have some unintended current draw going on.

If they work fine until and then just simply fail at the 9-12 month mark and cannot be recharged, then the batteries are most likely defective.

Less than a year on a battery, maintained on a tender or not, shouldn't be happening. There's a problem somewhere.