For a ship to move, maintain gravity, life support, weapons, shields and all its other functions, it must have a power plant (Energizer) to generate the energy needed to run everything.
Colonial ships use one of two types of power plant and require the corresponding fuel.
Older Colonial ships, those built more then two hundred yahrens ago, primarily employ Hydrogen Fusion Energizers These require purified hydrogen for fuel and work by fusing hydrogen atoms and harvesting the excess energy.
Beginning about 150 yahrens ago most Colonial ships were built using Solium fuel. This highly toxic liquid is refined from Tylium Ore and is a far more efficient fuel in terms of mass required vs energy output. Older military vessels, like Galactica and Prometheus Aegis, were converted to Solium plants but often retained their Hydrogen Fusion Energizers as back up systems. Newer military ships and most commercial ships were built to operate strictly on the Solium system.
The power requirements of a star ship, and its fuel consumption, can be prodigious. Most civilian/commercial ships are built on a budget, meaning that the smallest energizer feasible is the one used. The designers will first ask themselves what the ship will be used for. This dictates how fast it needs to travel and how far it needs to go with each Hyper Speed Run. Since the energy requirements for Hyper Speed are enormous, a common cost saving device for civilian ships and some small military vessels, was the Power Bank. These arrays of batteries are slowly charged by the energizer’s excess capacity when it is not being used. This energy is then used, in combination with the energizer out put, to power the ship at Hyper Speed. When the Power Bank drains out to the point that the combined power sources can no longer maintain Hyper Speed, the ship drops out of FTL speeds and returns to the sub light speed it was at prior to engaging the FTL drive.
Few civilian designers allowed much extra energizer capacity for weapons, consequently the Power Banks are also utilized to power energy weapons. This often means that firing more then a few shots will prevent the ship from escaping to Hyper Speed.
Electronic Defense Fields, or ‘Shields’ are even more of an energy drain and are found only on very large civilian ships with massive Power Banks and energizers.
Military vessels were not built with commercial budgets and needs, but even they have limits to what their Energizers can power, so Power Banks are also found on warships, but here they are used to supplement the Energizers which are usually capable of powering a ship through long or continuous Hyper Speed Runs. In such a case the limiting factor of a run is usually navigation rather then energy.
The Fugitive Fleet has added extra Power Banks where ever space and facilities allowed. This was done to allow civilian ships that were previously unarmed to have some extra defensive ability.
The Cylons employ Tylium/Solium fuels for their ships. The fact that they have few, if any, lifesupport requirements goes a long way towards improving their energy efficancy.