Speedo reading 3x actual speed after batter change.

I've just had the same thing. Left lights on, now speedo is stuffed.

Will write to my local Yama dealership here in Sydney and see what they say.

I went a head and replaced the display/meter (part#3D7-83500-51-00, it fixed the problem with both the speedometer and odometer. I now know how fast I'm going and the mileage is being recorded correctly. I purchased the part new from Yamaha at a cost of $260.00 us. It took me about 20min to install. FYI upon install the odometer will read zero miles.