[fomine3]

Fuel cell (and tank) is a different tech but car industry believe that it can be still manufactured at competitive cost and quality in Japan. It's hard to compete with Chinese massive amount of cheap batteries in Japan.

[starfallg]

Japan together with South Korea was a leader in NiMH and Lithium based battery chemistry during this period. So that wasn't the reason.

[fomine3]

Make it massively and cheaper is different to developing better one. So they now try to developing solid state battery but who knows will it success.