How to open seat with a dead battery on a 2013 Kymco Downtown 300i

They are usually an inline fuse on the wire behind it.

You could ask them direct, or google
make model manual
or
make model wiring diagram
or
make model accessory socket fuse

https://www.kymcohealthcare.com/?q=products

I did find this which has the answer!

12v power outlet fuse - KymcoForum.com

https://www.kymcoforum.com > ...

Mar. 5, 2016 - KymcoForum.com »; Scooters - 125 to 300 »; Downtown 300 »; 12v power outlet fuse ... I blew the fuse in the 12v power outlet so have taken off the front to change it. ... Hello zenith9, you're right, that is the fuse holder, I think it is a 'push together and turn anti ... '11 Kymco Downtown 300i ABS - 79,500km
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bad fuse ? if u have light try to take out of gear maybe start in gear function bad or try to short starter relay

charge the battery fully it may not have enough charge to start, you could jump start it with a battery or a car but not a running car, they put out 16 volts and will fry the electrics,

check cableling and fuses

the fuse is under the front plastic cover take it off and install a dash mount fuse in the glove box, beside the outlet plug it has # 20 wire in there, ask electrition how big a fuse you can put in there, or install wire from the battery with # 12 wire, and close the small wire off,