1980 KZ250 battery wont charge

Hello all, first time here.
I have been having an issue with my 1980 kz250 for some time now. The battery does not receive charge. I rev the bike to 3-4k revs and the battery voltage stays around 12v, not raising one bit.

Here is what I HAVE done so far:

****Replaced the stator (turns out the original one was working just fine, the stator has correct voltsge and resistance coming out of it, so the problem is somewhere in between the battery and the stator output)
****Gotten the battery tested at Advance, it checked out.
****Tested the regulator.

Please let me know if anyone has ANY suggestions, I am getting desperate at this point. I have not changed the fuses but they look to be fine. Everything on the bike powers properly when the battery is charged, but the battery will only last about 45 minutes on a full trickle charge.

How did you test the regulator?
The regulator is the device that converts the AC voltage from the stator into DC voltage and then charges the battery. It should be outputting around 14.5V DC if:
a) The stator is outputting ~70 V AC
b) The stator is correctly connected to the Regulator/Rectifier (RR)
c) The rectifier portion of the RR is converting the AC voltage to DC voltage
d) The regulator portion of the RR is regulating the DC voltage to around 14.5V DC.
e) The RR is correctly connected to the wiring harness
f) The RR is correctly grounded

Click on "Search" above
Enter the word "Electrosport" in the search box
Check the "Filebase" box where it says search in.

This will give a charging system fault finding flow chart which I have found very helpful in the past.
Good luck.

Just in case.... By any chance did you inadvertently connect the battery backwards?
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The manual for the 81 650 says that if the battery voltage does not rise as the engine speed increases, check the alternator & R/R to determine which part is defective. Try checking the alternator wires at the R/R connection to make sure alternator voltage is present there (AC voltage). Then check the power wire from the R/R to see if you're getting DC voltage output there (I think it will be a white/red wire w a bullet connector).

As suggested by JR .... Electrosport Technical Articles & Electrosport Fault Finding Chart