Shropshire Phone Repairs in Wem said phones and tablets brought in during the heatwave often show internal moisture damage after owners try cooling them in fridges or freezers.
Jamie Farnell said the shop is being "flooded" with heat-related repairs and that nine times out of 10 customers with swollen batteries or dead phones say they tried the fridge trick.
June's heat already produced glitching devices, expanding batteries and one iPad that exploded in the shop after arriving with a swollen lithium battery.
Farnell blamed social-media cooling tips for the practice and urged safer steps instead: keep devices out of direct sun, switch them off, avoid overcharging and cut processor-heavy use.
Electrical Safety First said overheating can break down lithium-ion batteries and trigger thermal runaway, a chain reaction that can spread between cells and start fires.