When: Your power meter is part of your drive train and should be treated as such. Anytime you clean and lubricate your chain or cassette is a good time to clean your power meter. This might be as simple as wiping it down, or giving it a full blown bath.
How: Mild soap and water, or a non-corrosive bike cleaner is best when cleaning your power meter. Use a brush or rag to lather up and scrub, and then hose it down to wash it all away.
PRESSURE WASHER: If using a pressure washer, it's best to AVOID spraying the power meter directly for ANY duration of time at close distances. Be sure to hold the nozzle far enough away that you're able to rinse, but not so close as to potentially force water into the power meter.
High Salt Environments: If your power meter sees a lot of salt, its best to wash it down pretty regularly. Salt can be corrosive, especially when an electrical charge might be present from the power meter's battery.
Indoor training - We're all for it! But even with fans the sweat rate can be high. Believe it or not, sweating all over your bike during the long winter can be pretty damaging. We recommend rinsing things down weekly. A sweat guard to shield your bike isn't a bad idea either.
Salts from sports drinks - There's a lot of salt and other sticky stuff in those drinks. If you miss your mouth or leave the top 'popped' chances are it falls between your legs right onto your top tube and crank set. If this sounds like you, be sure to give your power meter a clean whenever things start looking sticky!
Road salts during winter riding - Keep it up! Riding outdoors through the winter is no easy task and we applaud you, but keep in mind what you're riding through. The crank set sits directly behind a very capable road spray apparatus - your front wheel. When the roads get a bit salty, be sure to keep things clean. Your bike mechanic will thank you.