Yes, ACCUMULATOR is a Scrabble word!

Letter values in Scrabble US: A 1, C 3, C 3, U 1, M 3, U 1, L 1, A 1, T 1, O 1, R 1.

Is it a valid word?

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

a person who is employed to collect payments (as for rent or taxes)
a voltaic battery that stores electric charge
(computer science) a register that has a built-in adder that adds an input number to the contents of the register

Also: storage battery, accumulator register.