I have this every once in a while, but only when connected to the charger. Everything else is fine, so I did not worry too much about it.

With BatteryGraph, I can see that sometimes the load goes through the roof while this happens, but I have no idea, which process(es) cause this.

Healthcheck is okee, root and reboot works just fine, so I do not worry too much about my N900 for now.