Users do not need to enter a credit card to create a Tanki Online account. A player only needs to enter a credit card if he chooses to make in-game purchases of crystals, according to the end-user license agreement on tankionline.com.
Crystals are the currency of the game and are used to purchase repairs, upgraded weapons and other advantages. Players can purchase crystals or find them on the battlefield in the form of gold and white boxes that fall from the sky. Players also earn crystals in various ways, such as winning battles, referring a friend, receiving daily bonuses and participating in special contests and competitions, says the forum at tankionline.com.