The main idea is to set in and out the LiPo battery easily, saddle in my case, and to obtain a recurrant position of the X-brace to avoid adjusting the turnbuckle.

Here is the proposal.

A s batteries can slightly vary in height variables, add a thick layer or self-adhesive thick foam.

To avoid the X-brace to fall on the blue columns, a large diameter M3 shim need to be set here.

Next, I used some aluminum servo washer from T-Work's. Those shims have a shoulder underneath, shoulder with a diameter matching the holes of the x-brace.

Four long screws are needed to set everything together, explanation later.

The small o-ring is not mandatory, this is only a practicality.

Like so, once the screws tighten, the X-brace stay at the same height

To remove or install the batteries, the screws need to be loosened but not removing them, to slide the batteries from one side and then tight back the screws.

One set, the batteries are laterally locked in position by the carbon fiber chassis stiffener and vertically by the self-adhesive foam on the x-brace