I'm now the proud papa of a used British "Valiant Roamer", courtesy of EBay: https://www.ebay.com/itm/283072424577
Never heard of these until someone asked about one in SERVO's "Mr. Roboto" column. This is the first version AFAIK. http://www.valiant-technology.com/uk/pages/roamer_home.php?cat=1&1
It uses a classic 6V SLA battery, which I'm prepared to replace. These 4A types can be found online cheap, until you add shipping for such a heavy battery. Home Depot has these for $8.69 (and several other SLA types), with free ship to your local store. https://www.homedepot.com/p/UPG-SLA-6-Volt-F1-Terminal-AGM-Battery-UB645/203770472
These batteries aren't high tech, but they are still useful for some robots. Maybe not flying drones.
Chargers can be had for as little as$4... https://www.ebay.com/itm/1-pcs-6V-Volt-500MA-Sealed-Lead-Acid-Rechargeable-Battery-Charger-US-Plug/322939016979
"When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."
- Pablo Picasso