2008 Polaris ATV Sportsman 300 400 H.O. Service Manual, Page 213Get this manual
ELECTRICAL Battery Off Season Storage
Whenever the vehicle is not used for period of three months or more, remove the battery from the vehicle, ensure that it's fully charged, and store it out of the sun in cool, dry placeCheck battery voltage each month during storage and recharge as needed to maintain full chargeNOTE: Battery charge can be maintained by using Polaris battery tender charger or by charging about once month to make up for normal self-dischargeBattery tenders can be left connected during the storage period, and will automatically charge the battery if the voltage drops below pre-determined pointNOTE: The Sportsman 400 H.Ois pre-wired from the factory with battery charging harness (see Chapter "Maintenance" for location and charging information)
Charging Procedure (Low Maintenance)
If battery voltage is 12.8 or less, the battery may need rechargingWhen using an automatic charger, refer to the charger manufacturer's instructions for rechargingWhen using constant current charger, use the following guidelines for rechargingNOTE: Always verify battery condition before and 12 hours after the end of charging