What to do with a drone battery that has been exposed to water.

Do not charge or fly a battery with suspected water ingress until you inspect it. Moisture inside a pack can create a short between cells, and charging or flying before you know what is inside the case turns a recoverable battery into a fire risk. Set the pack aside somewhere open and away from anything flammable until you can work through it.

Begin the inspection by separating the cover and cells so you can see the pack's internal condition. A visual check of the outside of the case tells you nothing about water that has already worked its way in. 

Dry the components fully before going any further, then inspect them for corrosion or damage. Look at the cells, the contacts, and the connections for discoloration, residue, or any sign of swelling. A pack that looks dry on the surface can still hold moisture in the seams, so give it the time it needs rather than rushing it back into the charger. 

If you find corrosion, swelling, or any damage during the inspection, do not return the pack to service. Handle it as a damaged battery from that point forward and follow the battery swelling and disposal guide for the correct next steps.

Any fire, heat, or burning smell should be treated with extreme caution and taken seriously. If the pack has produced heat, smoke, flame, or an odor at any point, do not power on the drone and do not fly until a full inspection and work-through has been completed. Contact your dealer or ASD support before putting the aircraft or the battery back into service.