Duracell Procells are known to be more resistant to leaking than other alkaline batteries, but leaks and subsequent failures can happen with any battery.
The most common thing to encounter with a leaking battery is potassium hydroxide. This stuff is toxic and needs to be handled carefully. Time is of the essence in order to protect your electronic device or flashlight.
Potassium hydroxide is formed as a gas in the battery, the the increase in pressure can cause the battery seals to fail. Then you have a leak.
Cleanup is not hard, but needs to be done with care. Rubber gloves and eye protection are essential.
First, neutralize the leaking chemical with lemon juice or vinegar. Remove the leaking battery and carefully dispose of it. Swab the area where the battery leaked with vinegar. Don’t use water.
Once you have removed all the chemical spillage, rub the battery contacts with a pencil eraser in order to allow god conductivity with the replacement battery.
Electronic devices that will be out of service for an extended period of time should always have their batteries removed as a precautionary measure.