Hi. I think that would totally depend on the network/provider in use.
Quick data point: Among other Peplink products, we have a Balance with AT&T 4G modem attached to the USB port. When in “cold standby” no data is used – as expected. However, when in “hot” standby mode every morning in the middle of the night it uses very roughly 10MB of data. Other than that roughly brief exchange in the middle of the [local] night it uses almost nothing – the rest probably mostly from ICMP packets (not much).
So, I strongly suspect that this issue is “Peplink independent” (other than ping traffic, over which the user has total control as to frequency) and is really a function of the network in use.
Others are, of course, invited to correct/clarify my comments.