Yes the battery was drained
Output to the battery was all over the place, from 12.5 to 19v
If less than 'normal' can be several things - however if it is >15V then the R/R is DEFINITELY bad
I checked the RR voltage with it uninstalled
Not sure what you mean - how can you check the R/R Voltage with it not installed????
I also checked the wires going back to the stator while the bike was off and they are open
When you say "open" ......
What you need to do is measure resistance between ANY
one of the three wires to engine ground - this should be infinite resistance (i.e. "open" circuit)
If you measure between any
two wires, you should measure close to zero ohms (i.e. "short") - maybe something like 0.5 ohms but will vary by meter type
The important measurement here is the resistance (more correctly "isolation") to ground
If it passes the isolation test, then your stator is most likely good; if it fails (you measure short to ground) then it is toast.
There is really no need to measure voltage, the isolation test should suffice; if it passes or fails, there is really no need to test voltage;
however if you want to, you can measure AC volts (MUST be AC, NOT DC) between any two of the wires (with the R/R disconnected);
at any given rpm, you should read very close to the same between all three permutations of pairs of the three wires;
if there is any significant deviation between different pairs, the stator would be bad - however it would be extremely rare, HIGHLY unlikely that you would get a difference in one phase WITHOUT also having a failure of the isolation test.
Can you disconnect the battery while its running and see if it stays running, like an old car?
No.