My 24 volt battery operated Black & Decker mower suddenly quit?

I can read 24 volts with multi-meter across the battery terminals. I think the switch failed. But it is a mechanical contrivance and a sealed unit. B&D Repair says the battery is likely dead. I think they just want to sell me a new one. When plugged in it's charger still shows a green light. The status meter never did work right.