An alternative, cheaper way is to use limit switches to limit the westwards travel to that which allows the east facing panel to catch enough sun in the morning to bring the array back around. It doesn’t matter if this happens slowly because there’s an oblique angle - it just needs to happen. You don’t need the array fully perpendicular to the setting sun, after all, so a limit switch there isn’t costing much at all.
An easy way to implement a limit switch is a mercury tilt switch in the circuit between motor and tracker panel, then just arrange the mechanics so the tilt switch is attached to a member which changes angle as the array motors around.
The popcorn icon in post 2 refers to the fact you’ll likely have plenty of people wanting to talk you out of the idea, but I reckon you should go for it and hope you’ll start a build thread on here.
ps.. if you do go with your battery idea, maybe a 20V battery is over the top? Assuming you have your two small east / west panels wired in opposition to one another, the motor only ever sees the difference voltage between them - a lot less than 20V.