Maybe electric bikes and mopeds/scooters? Space seems to be a bigger issue for those than cars. And in the early days (and in some cases today) lead acid batteries were used. Lead acid had similar weight issues, but are much worse in terms of size and power, so seems like if folks were able to make that work, then a bike or scooter with this solid state battery could work.

I went on amazon to look at some product weights. There is an e-bike battery that weighs 6.5 lbs[1], and an e-bike that claims to have a shipping weight of 60 lbs[2]. So assuming 3x battery weight for roughly the same power, that means an extra battery weight of 13 lbs and a total bike weight of 73 lbs for a battery that could possibly fit in the frame (as opposed to be mounted on the down tube). So that is definitely getting on the heavy side for a bike but the bike in question is also relatively 'over-powered' as far as e-bikes go (25 mi self-powered range, 350 watt motor). A lot of the sleeker/higher end e-bikes are 'pedal-assist only' and already hide the battery in the frame. These bikes can get in the sub 40 lb range, and probably use 1/2 the battery that the one in the link does. So an extra 10-15 lbs is probably manageable and it would result in a bit more range while still being able to hide the battery in the frame (assuming a li-ion battery weight of ~3lbs, you would add an extra 6lbs to 'break even', or an extra 15 to double the power).

For scooters/mopeds, the math probably works out even better, as these are already over 100 lbs, and an extra 30-40 lbs won't really matter that much. And if you want to build a electric scooter or motorcycle that can go highway speeds, that extra weight can help with stability.

[1] https://www.amazon.com/36V-11AH-Li-ion-E-Bike-Battery/dp/B01... [2] https://www.amazon.com/Addmotor-HITHOT-Electric-Bicycle-Susp...