If you’ve determined your battery is dead and is too weak to start the engine, you’ve got to charge it. Getting a jump from another vehicle is an option. Here’s how to do it safely:

1. Make sure the dead battery isn’t frozen
2. Keep cars insulated from each other
3. Connect +ve jumper cable from good battery to dead battery
4. Connect the -ve jumper cable from the good battery to the engine block or a good ground away from the dead battery to avoid sparks.
5. Start the booster car (with the good battery)
6. Run the booster car for 10 minutes at 2000 rpm to invigorate the dead battery and warm the electrolyte
7. Start the bus with the dead battery
8. Turn on the headlights and fan on the bus with the dead battery
9. Remove -ve jumper cable from good battery, then dead battery
10. Repeat above with +ve (this will prevent an accidental short with the cable)