irkli, 10 months ago

Also there is this device, mentioned on Reddit:

https://www.reddit.com/r/ebikes/comments/ttznio/how_i_charge_my_ebike_battery_to_80_using_a_cheap/

https://www.icstation.com/m604-charge-control-module-battery-protection-board-controller-lithiumlead-acid-battery-solar-panel-p-11314.html

Given I have a decent un-smart controller, this may be a choice for folks like me willing to wire and package it.