White Crystals and powder on the battery is potassium carbonate.
This is electrolyte (potassium hydroxide) which reacted with O2 to form Potassium Carbonate. In this condition the battery is no longer usable. Potassium carbonate is a very strong alkaline and water soluble material. If there is skin contact there is a chance of chemical burns.
Please irrigate exposed skin with copious amounts of clear tepid water for at least 15 minutes. If irritation, injury or pain persists, please consult a physician. In case of contact with the eye, there is a risk of blindness. Under no circumstances you should rub the eyes. Flush the eyes with copious amounts of clear tepid water for at least 30 minutes.