That's not the battery light -- it is the PTO / Mower engaged light (tells you that the PowerTake Off is engaged) and if the mower deck is mounted the mower blades are engaged. :thumbsup:
OK - I could be wrong, it might be a battery / charging light.
While I'm here anyway, I wish they would use blue, red, and white instead of yellow, red, green -- especially when it is a single light (like on a charger) that is supposed to change from red to green when finished.
About 30% of the Male population has some colorblindness issues. Mine is red/green and I can't usually tell them apart.