Yamaha BIGBEAR YFM400NM Owner's Manual page 149

7. Remove the battery and charge it.
Store it in a dry place and recharge it
once a month. Do not store the battery
in an excessively warm or cold place
(less than 0˚C (30˚F) or more than 30˚C
(90˚F)).
NOTE:
Make any necessary repairs before storing
the machine.
9-4