I am in need of an adapter that will convert an ethernet port into a wireless access point. I have found a handful of devices, but I'm unable to find a device that is battery powered.

Does a self-powered wireless access point even exist?

The particular scenario that I will be using the device for is not your typical computer/PC scenario.

For the curious, here's a bit of background on the problem I'm trying to solve:

I make devices (controllers) that monitor water systems. Our controllers have a Webserver that serves out web pages so that users can configure the controller's settings. Typically, the user will use a cross-over cable to connect directly to the controller's ethernet port with their laptop to gain access to the controller's web pages.

Now that tablets (devices that don't have an ethernet port - iPad, for example) are becoming more common, I need to find a device that will convert the controller's ethernet port into a wireless access point so that the user can connect to the controller's web pages via Wi-Fi or Bluetooth.

It's worth noting that this wireless device that I'm looking for will NOT be permanently installed on the controller. It will be a portable device that the user will use on any of his controllers when he needs to make a connection to the controller.

If you know of a device that will solve the scenario that I mention above, please share your info.