How much data is redownloaded to my modem after an outage?

Good afternoon @user_ajs. Can you elaborate some more on your question? 

How much data is redownloaded to my modem and cable boxes after an outage? Does that data count against my quota?

Very little. Only enough to re-validate and reinitialize the devices. I would guess a few megabytes at most. Since data usage is counted by the gigabyte (1,000 megabytes), the startup data, if it is counted, is a rounding error as far as usage is concerned. 

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When your service goes down and then comes back up, there is a brief period of communications between your gateway and the node it is assigned to.  This is commonly referred to as a 'handshake'.  The controller queries your gateway, and your gateway provides the necessary information to establish a secure connection.  All of this does not generate a large amount of data, certainly not enough to have a major impact on how much data you have used.  Your gateway reboots on a regular basis, even if the internet does not go down. You will see it in the admin portal under "lease time", one for IPV4 and one for IPV6.  Even if the network goes down, and your gateway needs to install a firmware update when it comes back up, it won't eat up much data.

Thank you all for the clear explanation.