The lithium polymer battery pack of an ISF 5000 class solar car I worked on in undergrad. This suitcase-sized 35 kilogram pack, with a usable capacity of 5 kWh, is equal to four 8D lead-acids weighing nearly 300 kg.
There’s a good chance that you are currently sharing the room with a half-dozen or more lithium ion batteries. The computer in front of you has one, your camera has one, your phone has one, the R/C car your kid is racing around your ankles has one. Lithium battery technology is almost everywhere. And, soon, it’ll be coming to a boat near you.