HP hoses and o-rings also can and do fail, and, once again, divers are trained to look for signs like the rubber bubbling. There is also not really a difference between the o-rings used in HP and LP hoses and equipment outside the size, and I gave examples of LP hoses failing.

These all require regular maintenance and replacement, and, once again, divers are trained and should be checking their equipment regularly.

But that's all beside the point, which is that your claim is that "[o-rings] are extraordinarily reliable". Except they are not, they require replacing all the time. They may be industry standard, but they are fall from infallible.

Yes. Every couple of years. After being subjected to a lot of pressure cycling.

If you do nothing but take it into the shower or a swimming pool the o-rings will last longer than the batteries.