I recently replaced the battery in my older model (like 10 or so years old) cordless telephone. One of the warnings is to use their brand of battery to replace it, or risk explosions.
I know this is partly/mostly to get the company more money, but I was wondering: what is the basis of this warning? What about the (wrong) battery, exactly, would cause an explosion? I assume it has something to do with the voltage; the third party one I used as replacement has a range in which the old, worn out battery falls (500-800, and the old is 600).
That number you quoted is the capacity, probably in mW-hrs or mA-hrs, not the voltage.
But your are correct that the voltage is the problem. If you install a battery pack with a lower rated voltage than the original and the put the phone in the charger, the charger will still charge it at the higher voltage, and this can lead to fire, explosion, etc. The risk of this is higher with lithium-ion batteries than with the NiMH batteries your phone likely uses, but it is still present.
Overcharging the battery can cause chemical reactions, leading to explosions.
I’ve seen it happen in extreme situations - hooking up a 12V car charger to a phone as a regular charger, with the terminals reversed. Phone chargers, FYI, tend to run 5V. Even then it was more of a “let the smoke out” event than a true explosion.
I’ve also seen it happen with you use a battery with the wrong chemical makeup for the charger.
Modern devices have many levels of safety built in, so you are probably safe. I personally use third party batteries in my camera, for instance. But do so at your own risk.
Just a few years ago there was a huge deal in the media about 3rd party Sony and Apple laptop batteries exploding in laptops. You don’t remember that? There was some spectacular footage of one of the Macs going up in a conference room-- I’m not having any luck finding it now.
Anyway the phone maker’s just saying, “hey if you buy cheap-ass Chinese batteries, it might explode, not our fault”.
I’ve worked on mobile products that actively validate that you are using the right battery. Part of this may be a profit motive. Part of this may be that the device manufacturers don’t want customers to get hurt. Part of this may be that device manufacturers don’t want people to think their devices explode.