Battery Interval

I dont' see any recomendations in the manual. 

Based on it being a Lead-Acid battery, I would suggest annually or 2 years at the most.

Battery situation:

Hi Deana, Hi Chris,

Do test: check with digital multimeter (the best way, is with Analog based on 20Kohms but very good precision one) in charge and operation mode how many volts you have when full green show correctly fully charged.

Let multimeter, in continuum connected when check battery volts and disconnect immediately the plug from socket wall and, if you see voltage drop faster from 13.2 volts until 10 seconds, it's time to change battery. See on seller if give you access to date time for a new battery and the best max of months can be 1 or 2 in those days from when get out from factory not from storage. Yuasa is the best or, on which brand you trust with your experience. Today many honest brands have stopped to made a lot of kind of batteries because of transport Corona situation and maybe the trusted ones make immediately when customer wants to buy because that way, is correct for sell to customer.

All respect,

Mihai.

Also, 14.3v- 14.6v must be on battery when fully charged with plug in from outlet not more than that.