Madam had an Ipad4 for Xmas and as it's our first Apple product there is a quite steep learning curve for me

Does anyone know about MiFi? 'cos SWMBO will want to take it on holiday later, she's hooked on scrabble, and the hotel wifi doesn't cover the pool area.
I have looked into it a little and can see the attraction of a month's coverage, whereby you buy the gadget and then have a paid for limit, but I can't find how it is powered, is it a li on battery? and more importantly, do they do what it says on the tin regarding coverage and speed?
(By the way, it's needed in Cyprus

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Regards, Den.