I have this same problem on a 2009 street bob. Let me know if you find an answer. Mark
Something is on draining your battery overnight. Any light or any relay. It can also be your battery has a dead cell draining it overnight.
Either you have a bad battery or you have something draining it down overnight.
Either something is draining the power - or the battery is at the end of its useful life.
on the left to the rear of the seat (sportster)
Then either something is on draining the battery or the battery has a dead cell draining all the rest and must be replaced.
Can be a dead cell in the battery. If so the battery will have to be replaced. Can also be any light that is pulling power from the battery. Check all lights. Under hood, glove box, dome light, trunk, etc. Disconnect the negative battery cable overnight and if the battery is dead then the battery has a dead cell and must be replaced.
Have you had the alternator tested? Often a bad internal diode can drain the alternator overnight.
It can be any light in the car. Dome, glove box, trunk, under hood, etc. It can also be a relay that is stuck closed. It can also be a dead cell in the battery which will cause it to loose it's charge overnight. Have the battery tested at anyplace that sells batteries.
12.
Next to the battery.
A short will not drain the battery it will blow a fuse. It may be the battery has a dead cell, or some light is on draining the battery. It can also be a stuck relay.
It could be a dome light. To find out what is draining the battery overnight you need to take off the negative battery terminal and put a test light or Voltage tester between the 2 terminals. With everything off and all the doors shut or open if you have the dome light turned off, the test light or voltage tester will light up or show voltage. Go to the fuse block and take a fuse out one by one. If the light goes out when you pull a particular fuse, then that is the circuit that is draining the battery and you can take a closer look at it.