Piano Keyboard

Anyone aware of a cheap portable(batteryoperated) simple piano keyboard with big or standard keys?

I currently use an ipad piano app with my relative but he can only keep the beat with one finger on such a small screen. I really want something that sounds convincing which will make him try to use more than one finger. His hands and fingers were affected badly but I want to push him into trying harder with two hands. He was able to play the piano (sort of) prior to the stroke. Anyone located one and had any experience using such a keyboard? Most of what I see online are over complex.

My experience is with a mini-key 4 octave USB keyboard supplied by M-Audio. It works with the iPad to USB adaptor from Apple or third-party suppliers. Works well, and it also works with free GarageBand software. You can buy a full-size keys MIDI USB master keyboard I have one from M-Audio. I think it will work with the iPad, but you need a power supply in there somewhere. 

Thanks Rick I'll investigate. Apologies for the delay in responding but I don't visit the site by default. I had thought I would get an email notification to view -obviously not.