Looking forward to the review (especially if you post one on the store - hint hint
)
It's really unlikely that the rain caused any issues. The bike is very rain resilient although, as memory serves, the kill switch can at times be problematic but this is common on all bikes. The coil wire, in particular, is located in a really nice location, it's unlikely that water of any significant amount would get in there unless you ran around without your front fender on
I get that you don't want to hear about it being the battery so here's an excerpt from the Service Manual on how to make sure the charging system is working well. If it is, then it must be something small, square, and heavy
CHARGING VOLTAGE INSPECTIONRemove the single seat
Open the battery case cover
Be sure the battery is in good condition (fully charged) before per-
forming this test.Warm up the engine to normal operating tempera-
ture.
Connect the multimeter between the battery posi-
tive (+) and negative (–) terminal.
• To prevent a short, make absolutely certain
which are the positive (+) and negative (–) termi-
nal or cable.
• Do not disconnect the battery or any cable in the charging system without first turning the ignition switch OFF. Failure to follow this precaution can damage the tester or electrical components.
With the headlight high beam, measure the voltage on the multimeter when the engine runs at 5,000 minimum RPM
Measured BV < Measured CV < 15.5 V
• BV = Battery Voltage
• CV = Charging Voltage