The statement above about only using a HD battery would lead you to think that HD actually manufacturered battery's. We all know they don't and never have. The suppliers are on a bid basis, not necessarily low bidder but a bidder than can meet the spec's as noted on the bid form including ability to supply this product as needed, just like any other expendable they or any other vehicle builder uses. I recently purchased a Battery Mart battery online, I would probably have bought another HD but didn't want to drive to the dealer, 60 miles or so round trip when the Battery Mart unit was delivered to my door for about $80 less. Been several months now and I have no problem with it.
The same folks who will only buy a HD battery for their motorcycle, will buy a Interstate Battery for there $70,000 Denali and never think anything about it, so why differ for a bike.