Yeah, a small, brief spark when connecting the battery is common and usually harmless. It's just the electrical contact being made.
What's not normal is sustained sparking, large sparks, or a burning smell. If you see that, stop immediately. The cause is usually a short circuit.
- Check the battery terminals and the tool's terminals for debris. Metal shavings, dust, or other conductive material can bridge the contacts.
- Clean them off with the battery removed.
- Also, never store a loose battery pack in a drawer with nails, screws, keys, or coins. Those small metal objects can short the terminals, causing burns or a fire.
If that didn't work and the tool still sparks abnormally or doesn't run right, the tool or battery is likely damaged internally. Don't use it. Have it serviced by a qualified repair person using only identical replacement parts.
Heads up: Always make sure the tool's switch is off before connecting the battery. This prevents accidental starting and can minimize arcing.