Roombas run on NiMH batteries.

The PR2 I discussed in the blog post does indeed have a lithium ion battery pack. It has a 1.3kWh capacity, (188 times bigger than an iPhone 6's battery! Probably part of the reason the robot massed 220 kilos) which gave it a rated... 2 hours of runtime.

Lithium ion is better than earlier battery chemistries, but it's still not very good: https://upload.wikimedia.org/wikipedia/commons/thumb/c/c6/En...