Again, start simple.
There is a very specific way to install the battery on the 04 up sportsters. If not properly followed will result in the battery negative cable loosening up at the terminal every time .
1) Remove the battery hold down strap .
2) Remove positive cable from terminal .
3) Disconnect negative cable from the top of trans .
4) Slide battery out pulling the negative cable with it .
5) Tighten negative cable to battery terminal with cable pointing down.
6) Start battery into place feeding negative cable back in and down to trans .
7) Reconnect positive cable to terminal and install hold down strap .
8) Reconnect negative cable to top of trans .
9) Thank SCHMIDTYS for the write up
If that all looks Kosher, then start going through the charging system.
Charge System Diagnostics
Leave the gun. Take the cannoli.
borrowed from gtrman66
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