You need a total of $2.75 to get the batteries from the vending machine - your money is 2.50 and the quarter from Phil's market. The quarter is from the floor in the market by the drink machine (check your dime - it might be a quarter).
Then combine them all together in inventory to make a total of of 2.75 - not 2.50 and .25. The vending machine is picky it wants it all together in one shot, not 2 installments. Then, use the combined money on the vending machine.