By now everyone has heard of the hazards associated with Lithium-ion batteries -- fires and explosions in equipment as diverse as e-cigarettes, phones, quad-copters, and even Boeing aircraft. But the common alkaline batteries present hazards too! This one suddenly exploded with a fairly loud pop, blowing its top off. There was no smoke or flame or smell, so I couldn't immediately find the source of the sound.
Later, I found that it was connected into a low-power circuit a friend was experimenting with. Examining another batch of still-unused batteries, we found that another one had popped in a similar manner, even with no connection to any circuit.
Generally speaking, alkaline batteries are notorious for leaking corrosive liquid as they age, usually ruining the equipment they are installed in, so it's a good idea to remove them from equipment you value. Cheap batteries seem to be more prone to leakage. For example, in the past I've used Costco-branded AA batteries. In one case, an AA battery swelled and leaked, making it impossible to remove from a nice flashlight with an aluminum barrel. In another case, a pair of batteries were installed in-line, so when they swelled, the tops of the batteries were collapsed flat. I no longer use Costco batteries, but even the supposedly more premium Duracell batteries leak often enough that I routinely leave batteries out of expensive equipment.