USB host mode for RS232 data collection plus charging

I have a problem: I need a tablet which support USB host mode and can be charged at the same time - and it needs to be rooted. I tried both the Nexus 7 and the Yarvik 9-200 but in both cases I was not succesfull.

I am building an application that collects RS232 data via USB.

As I mentioned, I first used a Nexus 7 which worked fine. The issue however is that I need - USB host mode (to power the USB/RS232 convertor) - separate power supply (to charge the tablet as it cannot be charged via USB in hostmode) - Android 4.1 or better. The Nexus 7 could not be charged while in hostmode and therefore was not suitable. I checked a Yarvik 9-200 TAB (Xenta 97 IC) but I was not able to retrieve any data from the USB/RS232 port. Furthermore the original USB driver on their site didn't work which blocks me from upgrading the tablet to the new Android version.

Right now I am looked for a solution or another tablet. Is there someone out there that developped an application that collects RS232 data via USB