If you have the Interstate model you should have a continuous drain on the battery.
Old Post of mine:
I have a 2000 Interstate, 43,000 miles battery is not original equipment but I am uncertain how old it is. The bike has given me problems starting. So I have plugged in the battery tender overnight and the next morning it cranks over very nicely and fires right up. Ride to work and 12 hours later (yeah 12 hour days suck) it cranks very slowly and is barely able to start. Ride home is long enough to recharge it and when home it will crank very strongly. Until the next morning it is low again.
My initial thought was poor older battery not holding a charge, replace it and all will be good. So I ordered a battery and it came in Friday, today I thought that I should do a little more investigating to make sure it is a battery issue and not a charging system failure or a trickle discharge issue that can be corrected.
So I got out my trusty service manual and went to section 16
Voltage Inspection
Checked voltage of battery with bike off. About 12 volts ( a little low should be about 13)
Charging System Inspection
Current leakage test
Bike off, disconnect the negative terminal cable and put an ammeter in between the post and the cable. Current leakage initially was high and then as all the capacitors finished charging the leakage current dropped off to 2.2 milliamps (2.2mA). The manual states it should be less than 0.1 milliamps (0.1mA) so what I measured is a little high based on the manual. I think, however, that the manual states the appropriate value for the STD and Tourer not the Interstate. The Interstate has memory functions that draw current all the time in the dash for the clock memory and in the radio for the radio memory. I just do not know what they should be. Here is what happened when I unplugged the radio from the harness the leakage dropped to 1.0mA and when I unplugged the dash it dropped to zero. Plugged in the radio again and leakage went to 1.2mA and then plugged in the dash and it went back to 2.2mA.
Reconnected everything and started the bike and checked battery voltage with bike running. 13-14.5 volts depending on RPM. Seems right based on the manual so that confirms the alternator is working fine.
After a lot of looking for a problem, that was not there, the new battery DID solve the original problem, and I have had no issues, even though there is always a 2.2 milliamp draw on the battery.
I hope this helps
