Hi and thank you for your question.
If a new battery did not last very long, it sounds like your bike is not charging it.
The first thing you need to do is confirm that. Connect a volt meter across the battery, start the engine, observe the volts at an idle, then rev the engine to 4000 rpm and see if the volts rise. It should charge somewhere around 13.5~14.5 DCV.
If you are not getting that voltage in to the battery, we will need to check the stator and the regulator.
Start out by checking the stator. Find the rectifier regulator under the tank. It is the electrical component that is aluminum with cooling fins on it and 2 harness leads connected to it. Disconnect the lead that has the 3 white wires in it. Set your ohm meter on Rx1 and check all 3 white wires to each other (3 tests). They should have 0.14~0.18 ohms resistance between each of the 3 possible combinations. With such small resistance values make sure you cross your meter leads and record the internal resistance of your meter and subtract that value from the test results you get when checking the stator coils.
From there, the only component left is the rectifier regulator. The service manual uses a process of elimination to get to the point of indicating replacement of the rectifier. If you have a good battery, the stator passes the resistance tests, then it says replace the rectifier.
If you have any more questions, feel free to ask.