Everyone is looking for a solution but failing to see the problem.
The OP starts his bike, rides 20 blocks to work and shuts it down.
At 35 MPH, 20 blocks should take a little over 2 minutes.
To recharge a battery after starting a bike needs to run about 40
minutes. Repeatedly starting without sufficient time to replenish
is simply running the battery down.
The simplest solution, if possible, would be to connect it to a
trickle charger each night.
I am agreeing a lot with this answer. Charging cycle may just be too short.
Regarding load test of battery:
You have a load tester. It's called the starter motor. Put your meter in VOLTAGE mode, and connect it to the battery terminals, positive to positive, negative to negative. Crank the engine, (without using the enrichener), you want it to crank for a few seconds, but not start. If battery voltage drops below 9 volts, it has a problem. If voltage stays above that for several seconds, then battery is in good shape.
Also, check for parasitic amperage draw when the bike is shut off. Here's a pretty good discussion of how to connect your meter to check for any amp draw with the ignition switch off. You will get a few milliamps draw from the clock, you can isloate that by disconnecting the clock. There should be no other amperage draw. If there is, then disconnect one circuit at a time to find out what it is.
https://www.batterystuff.com/kb/articles/charging-articles/testing-your-battery-for-parasitic-load.html