Getting killed while on a killstreak will reset a player's streak to zero, and the opponent that killed you will receive bonus Joules. The number of bonus Joules depends on how large the killstreak was. This is called an "End Streak".
In battle, a player will be notified of their killstreak when they hit a streak of 3 or more each time they get a kill.
Each additional kill after the third kill adds 10 Joules. Whether the Joules from the killstreak are added into a pool (e.g. a 3 killstreak adds 10 Joules, and a fourth kill will add 20 Joules, making the total earnings 30 Joules for one streak) or are counted as the highest number before death (e.g. a 3 killstreak adds 10 Joules, and a fourth kill will raise the total earnings to 20 Joules) is unconfirmed as per this edit. The latter will be used in explaining. When a player with a killstreak dies, the Joules won are added to the player's earnings, and the bonus resets. When a new killstreak in the same round has been made, the previous killstreak earnings are kept in a pool, and the new killstreak, either at the end of the round or when ended, will be added to the pool. For example, if a player has a 5 killstreak, dies, and builds up another 4 killstreak until the end of the round, that player has earned 50 Joules. 30 from the previous killstreak, and 20 more for the current streak.
When a player kills someone with a killstreak, they will be rewarded with an "End Streak" bonus in addition to the normal amount of XP and Joules awarded. This bonus also depends on the amount of kills that player has made. The more of their teammates the player killed, the more Joules are given for killing the opposing player. So far, there is an indefinite maximum to the amount of Joules a player can get per streak ended. The way to calculate an "End Streak" bonus is to subtract the number of kills by two and multiply the result by 20 Joules. For example, if an opponent has a 7 killstreak, the player who ended his streak will receive: 20 x (7-2) = 100 Bonus Joules. The table below shows the number of Joules players will get for killing someone with a killstreak.