People inhabiting the biospheres suffer from the shortage of energy to power various devices. The energy cells are therefore especially valuable. They power many kinds of projectile weapon as well as hi-tech items. It led to the situation, that these energy cells became the official currency. You can buy everything for them. Luckily, a big amount of them is scattered in the biospheres and during hero's journey we would have a chance to collect a large number of them.