If you have a battery heated item that uses AA or D sized batteries, your batteries should be removed from the battery holder. If you do not remove the batteries, they could corrode and cause damage.
If you have a rechargeable battery system, READ YOUR OWNERS MANUAL! Many times the manufacturer recommends your batteries to be charged every 6 months while in storage. If not they will go into a dormant mode or sleep mode and the batteries completely drain of their charge and may not accept a re-charge thereafter.
So depending on the last day you used the batteries, we recommend charging your batteries on Memorial Day and Labor Day. Make a little time to take care of your batteries and you will thank us for it next winter.