I've been curious about Energy Vampire's 5% - 10% damage percentage. The last time I tested this, which was some time before U11, I was not able to determine a constant percentage of enemy health that is removed at every pulse of energy. The difficulty I had came from the observation that the percentage depended on the enemy's level, or at least that seemed to be the case.
It's been several months since then, so I wanted to see if the percentage has become constant. Since I'm relying on displayed damage values that are rounded down, I used Well of Life on various non-armored enemies followed by Energy Vampire. This way, the displayed value can be divided by 10 to yield an additional decimal place that I would have missed otherwise.
An enemy's health is calculated using the following expression:
health = base health + base health x 0.015 x ( current level - base level ) ^ 2
This value also appears to be rounded to the nearest whole number, unlike armor and damage.
With all of that said, here are some results. The first five columns should be self-explanatory. Since each tick inflicts slash damage, I needed to account for enemy resistances before estimating a new percentage. This percentage is defined as ( observed damage / health ) / resistance.
As enemy level increases, the percentage approaches 6.25%. The lack of internal rounding for large health values should explain this apparent convergence. This result agrees with the original 5% - 10% range, so let's assume this is the correct value. In order to test its accuracy, I created another column for the sole purpose of comparing observed damage values with expected values. As you can see, there is very good agreement between both columns. Here's an example so you can see how the damage is being calculated:
A level 15 charger has 315 health.
315 x 0.0625 = 19.6875
There appears to be internal rounding at this point, so throughout the spreadsheet I've assumed this portion of the calculation is rounded down to one decimal place.
19.6875 ---> 19.6
Accounting for the 1.25x slash damage resistance:
19.6 x 1.25 = 24.5
This value would also be rounded down to one decimal place, but as you can see there's no need.
Using the Well of Life / Energy Vampire combo against shielded enemies made me realize something. The 6.25% doesn't just apply to the enemy's remaining health; rather, it applies to the enemy's total amount of remaining hit points (including shields). Here's an example:
A level 21 crewman has 600 shields and 420 health. Using Well of Life followed by Energy Vampire, I'm noticing "375" damage being dealt to its health after shields are removed. Reapplying Well of Life, the damage tick is now "327". This tells me the shields were being used to determine the damage of each tick, which explains why less damage was inflicted when the shields were removed.
The crewman will have 600 shields and 4200 health under Well of Life. That's 4800 total hit points:
4800 x 0.0625 = 300.
Considering the 1.25x slash damage multiplier against flesh:
300 x 1.25 = 375.
As a final series of tests, I wanted to see how well the 6.25% holds up against low-level Grineer. In the second sheet you can see the results: there's excellent agreement. The final three rows are a repeat of the previous tests with +30% power strength. Again, the observations and expectations agree very well.
That's all I have. If you have something you'd like to add or ask, don't hesitate to leave a comment.