Can't play video if R40 is only on battery

[PapyMax]

When I want to play a video, if I use external power, there's no problem.
But if I unplug, after a few secondes, my computer get stuck. No sounds, nothing move. I have to shut down manually.

I tried several players, changed power managing...etc. Nothing changed.

Someone else had the same problem? Have you any tips?

Thanks.