I think you made the wisest decision.
I was recently out on the new bike 2010 ultra. Returned home and had an after thought to go check the trip milage, so out to the garage and flip the switch over to acc. checked fuel , remaining milage, trip 1 and 2 and total milage. I didn't plug into the battery tender and the next night I hear the siren go off.(siren has back up power) The siren sounded because the battery was totally dead. When I checked the milage I left the switch in acc mode. There was a CD in the player (volume muted).
The maintainer would not charge it after two days . I searched prices for a replacement battery and found about 150 average for a HD battery and about 110 for the non HD battery.
ultimately, I removed the battery and placed it on the fast charger for an hour, then switched to slow charge overnight, checked voltage next morning and had 13.5 volts.
I got lucky the battery bounced back and works perfect.
I now double check the ignition sw. and make sure I plug into the battery tender after each ride.
Going with the recommended battery is wise. I didn't research the cold cranking amps, output of the charging system yada yada and so on but there is way more to consider than getting the cheapest price.
A battery maintainer is worth investing in if you don't already use one.
The ebay route could be worth it but I find myself asking ,do I have the time and patients . Like what if ....what if some one ships a bum battery , now I have to fool around shipping it back , again yada yada