Limit CPU usage of a process?

Is it possible to limit the CPU usage of a given process to, say, 20%?

I'd like to slow down the web browser since it is draining my laptop's
battery. With enough tabs open it's often consuming ~50% of CPU but
not doing anything productive. Apparently with RLIMIT_CPU in
setrlimit(2) the total CPU time of a process can be limited. Can a
similar limit be set for the percentage?

Thanks