The correct answer is <em><u>A) At least once a year</u></em>
Explanation:
The battery and charging systems are very robust. However, they play such an important part that it is better to maintain and upkeep for maximum performance.
Once a year is an ideal time to check the charging and battery. If you have the time and expertise, you can obviously do it twice a year.
If you only do it once a year, it is better to do in the Fall, before winter arrives, so you are prepared.