A new battery????????
laptop or desktop? .... after (then) 21/2 years....
either way ... unless it's an exceptionaly unusual fault .... it sounds to me as if your little old lady has been taken advantage of.
I can count on the fingers of one thumb the number of batteries I've changed this year (the machine was at least 6 years old)
personally I favour a soft brissle brush....
a new can of air will often spit propellant (also if you shake it about or use it at an angle) ... they also tend to rapidly cool the air and components which can lead to condensation forming.
but ... if you must ... wear safety glasses 'cause a lump of muck accelerated by a jet of compressed air travels much faster than you'd think ...and feels more like a brick if it hits your eye.
as a matter of interest ... we've banned the stuff ... partly for the reasons above ... but also .. left on the passenger seat in direct sunlight ... a can of air will take out your windscreen quicker than a quick fit fitter!