Yes, CELLS is a Scrabble word!

Letter values in Scrabble US: C 3, E 1, L 1, L 1, S 1.

Is it a valid word?

CELLS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

any small compartment
(biology) the basic structural and functional unit of all organisms; they may exist as independent units of life (as in monads) or may form colonies or tissues as in higher plants and animals
a device that delivers an electric current as the result of a chemical reaction
a small unit serving as part of or as the nucleus of a larger political movement
a hand-held mobile radiotelephone for use in an area divided into small sections, each with its own short-range transmitter/receiver
small room in which a monk or nun lives
a room where a prisoner is kept

Also: electric cell, cellular telephone, cellular phone, mobile phone, jail cell, prison cell.