When you bought the new battery 3 months ago, was it or did you fully charge it before use? As others have said, tenders are not chargers. Take battery back and have it tested; then if OK, fully charge it. Also check bike for current draw when off after installing new battery.

 

Most batteries are fully charged when bought new. Furthermore, you should charge it before having it tested. Otherwise the store clerk will determine it's just bad and you'll buy another, but that may not be bad because the price should get prorated.

 

Bad battery. Even if not fully charged it will measure at 12-13v easily (voltage will show proper just not be full load capable). My new battery via online shipped at 50% charge and took full day to charge fully with HD tender off the bike.

 

so i noticed the terminals were dull grey, possibly some kind of corrosion. I cleaned them with a ball of tin foil and hooked up the battery to the charger again. 10 hours later and the charger is green. I will test the battery later but could oxidation of the terminals provide high enough resistance that the battery was barely charging?

 

Dull gray is not usually oxidation unless there's a buildup of crud. I used to cast fishing weights out of lead. When they were fresh out of the mold they were very shiny, but it didn't take long to look dull.

 

Update: battery reads 12.6V with no load. Bike starts right up.