Batteries are pretty well sealed as far as their inner components, and should be water tight.
However, on some batteries the protected circuit on the button top variety has air vent holes which might be harmed if exposed to water or other liquids. I'd attempt to dry them off and allow to evaporate before I'd use them.
this.
though, i'd add the caveat that if exposed to salt water, they should be rinsed well with fresh water with as low a mineral content as possible before drying. tap water will likely do in a pinch, but reverse osmosis / deionized or distilled water would be ideal. the harder the tap water (more minerals) the better it would be to search out an alternative.
think about it like clothes with a possible stain on them. the batterys are the clothes. the minerals are grape juice. if you throw the clothes in the dryer before removing the stain, it will likely be set in forever. only in this case, the stain is conductive, oxidating, ionic particles of minerals. running current through them hyper charges them and speeds the degradation of the cell outer walls and contacts by speeding the oxidation process.
plus, if the cell ever gets wet again in a device, the ions can travel. if they're in a regulated device at that time, it could be the difference between just a drop of water to be dried out and instant, certain death of the pcb.
