Display is flickering when when going in sleep mode (on battery only)

Hi,

This lap top has been repaired several times.

For the same phenomena, Inverter board has been replaced twice by a service company when the macbook was still under warranty.

I noticed this phenomena doesn't happen when the power supply is connected to the macbook.

Any idea ?

The macbook is running under 10.7.5

Thx,

Jérémy (France)