Some or maybe even most phones will survive, but there's a reasonable chance of the device going up in flames. Older batteries are even more likely to catch fire, depending on the type.

Phones and their batteries aren't made for this. Trying to run a phone 24/7 will likely result in the phone dying very quickly and raise the chances of it exploding.

There's an external mod manager that I forgot the name of. They have mod packs that are Semi-Updated.