Arcing - short question
 

I recently bought a used X-treme Baja 36 V bike. Spent the last week or so, cleaning, servicing the fork, general stuff. When I bought the bike, the PO turned it on, the motor spun, display worked.
This is a folding bike. When I went to reinstall the battery today, when the bike's terminals came into contact with the battery terminals the negative terminal arced. Do I suddenly have a short somewhere. Could the on/off switch
have broken when I worked on the bike and could it be broken in the on position? Could I have shorted the motor when I cleaned the gears? I have no idea how to even begin to look into where the fault might be.
Any suggestions welcome.

Nice

Often, power sources will arc if there is anything ON in the circuit. Did the bike still run? If so, no problem! If you have not tested it, if something has been damaged, the damage is done, and any testing should do no further damage.

Just my opinion.

It's in the nature of ebike batteries to spark when they are connected to the controller. Doesn't matter if the bike was turned on or off. The controller has some capcitance in it that will take a high inrush current from the battery as it slides in. That causes a spark.

If you had a battery with an on/off switch, but I don't think the X-treme Baja 36 V bike has one, you could turn it off before sliding it in. Then there would still be the inrush current when you turn on the battery, but no spark,

Sometimes the same thing happens when you plug in the battery charger,

Of course, sometimes you get a real fault, like a short circuit or someone reversed the wires. Then you get a real arc. Contacts melt. All kinds of bad stuff. Don't do that.