New Moto Guzzi Door Mats Available Now
Look around the house, see if you have an old 12 Volt wall wort from a printer or something.Chop the 12V connector off and connect the wires to the battery.The wire with a stripe is usually positive.Even it the battery is dead flat a wall wort will try to charge it.
What's a wall wort?
A wall wort is a plug in step down transformer like a cell phone charger. https://en.wikipedia.org/wiki/AC_adapter
This is important. If using a car or truck to jump, do not do so with the donor vehicle engine running. The high amperage current will damage your bikes regulator/rectifier. Bike components are not designed for 80 amps.