You'd probably have more help at
www.HondaRebel3forum.com
We know Gen 1 & 2 well. Generation 3 not as well.
A jump box would be just fine.
Generally, motorcycles need the voltage more accurately controlled than other vehicles, because 1) the battery is so small, & 2) the electronics are quite sensitive. If you do jump it, the other vehicle should always be off.