do not keep giving the right time vs stop giving the right time

Question

Clocks do not keep giving the right time if electricity goes off.

Clocks stop giving the right time if electricity goes off.

Which is natural and why ?

Answer 1

Assuming the clocks do not have a battery backup...

Clocks do not keep giving the right time if the electricity goes off.

means over a period of time the clocks are not accurate. The accuracy could vary from time to time. It would be assumed the clocks are still running, which would not be the case if the electricity went out.

Clocks stop giving the right time if the electricity goes off.

just means the the clocks will not be accurate once the electricity goes off.

In reality, once the electricity goes off, the clock stops. The second example is best here, because it can't be accurate until the electricity goes on.

However in the case where there is a battery backup, the situation will depend on how the clock maintains accuracy.

Answer 2

To keep in this context means to stay in a particular place or condition

It might be appropriate to say

Clocks keep giving the right time if the electricity is on.

Once the electricity goes off, you could say

Clocks keep giving the wrong time if the electricity is off.

but do not keep giving the right time does not mean the same as keep giving the wrong time: the negative is in a different place.

stop means that something was happening, but then it stopped happening. This is a perfect way to describe this situation: it implies that clocks give the right time while the electricity is on, and give the wrong time as soon as the electricity goes off.

Note that you can use the expression keep time when talking about clocks:

Clocks keep time while the electricity is on, but stop keeping time when the electricity goes off.