I like the answers given thus far from IMR & Degers...Since my Pleos and their chargers/batteries have been in a deep slumber/box for an unmentionable amount of time, I've recently experienced this firsthand, myself...

If you were like me and had dust galore all over everything, I simply grabbed a bottle of isopropyl alcohol, several Q-Tips/cotton swabs, and cotton balls. I applied the alcohol to whatever utensil I was using to clean, and squeezed out the excess since you don't want a large amount of alcohol entering into a tight fitting space in Pleo that may never dry.... I used the cotton balls to clean larger areas, like the extremities of the batteries/charging cradle and the interior of Pleo (inside his belly). The cotton swabs/Q-Tips were used for the smaller/harder to reach areas such as the contact points, and springs, as well as the seals around the battery itself.
I have also found alcohol to consistently be a good general multipurpose cleaner for Pleo. Sometimes it's easy to overlook regular cleanings. For that I use cotton balls for the skin (look at it after you clean it! Ew A LOT of dirt on Pleo's skin!!), for the tongue, eyeballs, feet pads, etc...cotton swabs/Q-Tips for the nose (where all his seeing sensors are!!), for the 'ears', and any other smaller/harder to reach areas.
From personal experience, alcohol has been a wonderful all purpose cleaner for Pleo!! Best of luck to you.