IMR 18650s are very light, will fit in pretty any much tube on a bike, potentially even inside a tyre on a tubeless job, and will push 80A for 120 seconds, which is a crap-tonne of power.
Having a battery assist is the difference between working hard for an entire hill climb, or being able to do 30 seconds on 30 seconds off and fartlek your way up the hill - which is the difference between winning and losing.
For the mass of 10 cells (500g) you can get 25aH - which works out as about 60W for an hour at 2.5v - which is enough to save you 10% of your energy expenditure over a one hour race if you're going hell for leather - which is still the difference between winning and losing.
Having a battery assist is the difference between working hard for an entire hill climb, or being able to do 30 seconds on 30 seconds off and fartlek your way up the hill - which is the difference between winning and losing.
For the mass of 10 cells (500g) you can get 25aH - which works out as about 60W for an hour at 2.5v - which is enough to save you 10% of your energy expenditure over a one hour race if you're going hell for leather - which is still the difference between winning and losing.