Pretty sure it is what the fellow upthread surmised, it is some kind of battery protection that is based on voltage sensing or heat sensing that goes awry. Don’t think a new battery or cleaning will help. Best thing is to buy a new vac rather than waste money on a new OEM battery which is close to half the price of a new unit of an older model on clearance.The non OEM batteries use cells that have been rejected by quality control and they are assembled haphazardly without any control circuitry (I opened one up) to achieve the low prices, I would not trust them to last very long.