simulating a Li-ion battery in parallell with a ultra-capacitor

Hello, i would really love some help with simulating a Li-ion battery in parallell with a ultra-capacitor to "cut" the current peaks for a random load characteristic(curve).

The point beeing to prolong the lifetime of the battery by cutting the current peaks with a ultra-capacitor taking over for the battery at certain limits.

Any ideas/solutions to this problem would be greatly appreciated! :)