Plenty of car drivers roll around with jumper cables , which will allow you to use the battery in their vehicle to get your bike cranking. Just find yourself a good Samaritan, have 'em pop the hood, and hook up the cables. First, connect to the positive (red) terminals on both vehicles. Then clamp onto the negative terminal of the good battery, but attach the other black clamp to an unpainted chassis part away from your bike's battery. The idea here is that, since the last clamp you connect is going to spark, you want it to happen away from the battery, which could possibly, potentially, maybe be emitting hydrogen gas due to its unhealthy condition. And, as the folks in the Hindenburg found out, hydrogen is flammable. You're not likely to have any issues, especially with modern sealed AGM batteries, but it's easy to minimize the risk to nearly zero by clamping somewhere safe.