Oxidation/corrosion at the contact points: Battery to battery, battery to body's contacts, switch... Marginal batteries: Sharp acceleration shifts internal c

Oxidation/corrosion at the contact points: Battery to battery, battery to body's contacts, switch... Marginal batteries: Sharp acceleration shifts internal contents just enough to provide for a more energetic discharge. In short, yes, it's a real thing. Especially when Dad insists on keeping his 50 year old flashlight and on eking every last electron out of each set of batteries. ;-)