Wikipedia
A Powerlet cartridge, commonly referred to as a CO charger, is a small disposable metal container holding of compressed CO and often a small quantity of oil, used as a power source for certain air guns, airsoft guns, paintball guns, and for quick inflation of sundry devices, such as a personal flotation device. Originally developed and the trademark owned by Crosman Corporation and introduced to the market in 1954, the Powerlet cartridge has become the dominant source of power for inexpensive, rapid fire air guns from many manufacturers.
The Powerlet container typically lasts between 20 and 40 shots in an airgun depending on the gun and environmental conditions. One can expect to get about 10 average shots from a new bottle, then every subsequent shot becomes less powerful. For paintball markers, one can expect fewer shots because of the increased weight of the paintball compared to an airgun projectile.
For modern paintball guns, this technology is considered outdated. However, some still use Powerlet cartridges for stock paintball, because they cannot fire as many shots as a modern tank can. They are also still favored for paintball pistols, for players wishing to run 'light', and offer considerable weight savings over a modern high-pressure air tank.