It is highly advisable to use batteries of the same type, brand, size and expiry date in one appliance. The electrical capacity of different types or batches can differ. If such different batteries are used the difference in electrical capacity will grow during usage which could eventually cause one of the batteries to over discharge, leak and even explode.
Never use old and new batteries together, as this may cause leakage or worse. The remaining electrical capacity in a used battery is less than a new battery, even when it was only used shortly. This causes that when used together with one or more fresh batteries, that this used battery will lose capacity and voltage faster than the new batteries, which could cause eventually an over discharge and leakage of that battery.