Yet another sump pump/check valve question

[RolHammer]

Plumbing noob here with a first time post.

My sump pump packed it in and I'm replacing it with both a new unit as well as a battery backup unit.

Now, I notice that the old pump didn't have a check valve. Clearly, this is a violation of the orthodox 'a check valve is needed to prevent the water from running back into the sump' rule. I'll be adding a check valve in front of each pump as part of this but am curious: what happens to that water that's standing on top of the check valve(s) after the last rain has fallen and temperatures turn toward freezing?

I see the point of having the check valve in the first place but wonder about those couple of gallons sitting in the pipe. I've searched around online and don't really see the issue discussed much. So, I'll be drilling the usual relief hole just below the check valve to prevent airlocking and am wondering if a similar small hole just above the check valve might address the other concern. What have others done?

[Terry]

Without the check valve, you will be pumping the same water over and over again. That's a good way to run up your electricity bill and wear out pumps.
If it's freezing, then you will need to insulate.
If this is in a crawlspace, then it's very doubtful that it would ever freeze.
In the Seattle area, I pump my mothers yard when it rains. It has a check valve without the hole drilled in. We run 150 feet of pipe to the public storm drain with about 15 feet of head. This drains three properties. One time the neighbor replaced the pump and left off the check valve. The water in the hole was getting pretty warm from cycling over and over again through the pump impeller blades. Or maybe it was the motor warming the water from the constant use.

[LLigetfa]

I did not put a check valve on my sump pump because I didn't want to risk freezing. My insulated sump line is a short run to where it breaks the surface and has an air gap. The amount of water that runs back into the pit is but a small fraction of how much is pumped out on each cycle.

My iron filter and softener both backwash into the sump pit and that keeps ice from forming after the air gap.