The Energy or Stamina bar represents the soldier's current level of tiredness. A full bar will mean that the soldier is not tired, while an empty bar means that the soldier is exhausted. A soldier's actions are limited by both energy and TUs; if you have depleted one or both of these stats, then you will not be able to preform any actions.
The primary actions that will consume energy are walking, or flying when wearing the Flying Suit. Some aliens will also lose energy when simply changing their facing. Changing your elevation by means of a lift or Flying Suit will not consume energy, nor will firing weaponry. Energy and Time Unit costs for walking will vary depending on the difficulty of the terrain being traversed and the type of unit that is traversing it.
Note that the soldier stat screen refers to the stat as Stamina, while it is referred to as Energy in the battlescape. They are otherwise used interchangeably.
New recruits will always begin with a value between 40 and 70.
Energy points are awarded (at end of mission) any time you perform at least one primary action. Just one action is enough - additional ones do not cause more points to be awarded.
The possible points earned are dependent on your current Energy. At recruit minimum (40 Energy), an average of 4.0 points are earned. This slopes evenly down to where, at cap minus one (99), an average of 1.0 points are earned (range 0-2).
A soldier's Energy caps at 100, but it is possible to 'overflow' the cap by one point on the last combat when you go over the cap. On average, you have a 33% chance of getting capped at 101 instead of 100. Once at 100+, all Energy/Stamina improvements cease.
Formula: Energy Used = INT( TUs_Used / 2unitref)
Example: All X-COM units have a unitref=1. Crossing a standard tile to an adjacent one uses 4 TUs. This means that they will use INT(4 / 21) = 2 EUs.
Aliens can have different values for unitref (depending on race - no one's bothered to document these yet). Many appear to have 0, which means they use a 1:1 ratio of Energy to TUs. Such aliens even need 1 EU to turn one facing (a 1 TU action), unlike X-COM soldiers. A few have been seen to have values of 2 or higher. With a value of 2, they don't use energy when walking to adjacent tiles, only diagonally. Values of 3+ result in little or no Energy usage; 4+ (24=16) will make even the most TU-expensive tiles (12 TUs) cost 0 energy.
Each fatal wound to the body reduces the soldier's energy by 10%.
A soldier's ability to recover energy is determined by the soldier's Initial Time Units. Thus, their raw recruit TU value dictates this throughout their career. You can see initial TUs on the Soldier tab (Strategic view) as the darker part of the TU bar.
Formula: Energy Recovery = INT(Initial TUs/3)
Example: If a soldier starts with an initial value of 60 TUs, they will recover 20 EUs per turn.
|Time Units||Energy Recovery|
|51 → 53||17|
|54 → 56||18|
|57 → 59||19|
Energy can also be recovered by way of stimulants from a Medi-Kit.
The stamina/energy stat displays erratic behavior in battles if pumped up far beyond the cap value, by using a cheat/editor.
Up to 179 (including) all is well. But if the stamina is set to 180 the soldier will start with zero energy and will be unable to move.
Each turn the energy level will fill up (providing the soldier didn't move around too much) but when reaching the infamous byte barrier at 255 it will drop back all the way to zero again.
Going beyond initial 180 stamina maintains this behavior, except that instead starting with 0 energy the soldier will start with (Stamina - 180).
It doesn't matter how the too-high stamina is formed - either the original stat pumped up, or the improvement stamina or combination of both.
|X-Com: Enemy Unknown/UFO Defense|
|Soldiers:||Time Units • Energy (Stamina) • Health • Bravery • Reactions • Firing Accuracy • Throwing Accuracy|
|Strength • Psionic Strength • Psionic Skill • Melee Accuracy • Stun • Morale • Rank • Fatal Wounds|