RE: What happened??? Multi-Tester almost fried battery pack.
It sounds like you had the meter set to measure Amps, then connected it directly to the battery. That creates a dead short.
To measure Amps with a meter like that, you need to put the meter in one of the lines. You want to measure the Amps going through the ESC and motor, not how much the battery can put out.
You would connect the meter across the terminals to measure VOLTS, but you'd need to have the meter set up to measure Volts.