If something is broken, giving it a good kick or a thump might make it work. True or false? (Well it all depends). Often with electronic equipment the so-called “technical knock” will get some things working but with motor vehicles it’s usually not worth the effort, except in the case of batteries, according to Burke’s Backyard scientist, Graeme Quirk.
As a normal lead/acid battery discharges it produces a substance called lead sulfate, which can build up on the battery plates and cause them to short out. A good thump can dislodge the build up and give dead batteries a new (but short) lease of life.