Having considered the problem and implications a little further, I've revised my thinking.
To prolong the life of modern phone batteries, the best approach is to incrementally charge the battery rather than rapid charging.
During my 50 min drive, with an Android Auto tethered connection (Waze & Music playing) my Pixel 7 charge increases by 10% - which is pretty much ideal.
Whatever happened to plans for Lexus to support wireless AA, how come wireless Apple CarPlay is supported?