Can I deactivate my Eldritch Cannon to "save magic battery power?"

This came up as my table was discussing various features and tactics, related to the Eldritch Cannon. I can cast it once per day for free, and again with a spell slot. Each time it is created it'll last an hour. Or, I can dismiss it early.

But battles rarely take more than three rounds (barely 20 seconds!). So the majority of the time is wasted, unless we happen to wander into another battle soon after.

So what do you think? Could I power down my cannon, stash it in a pack or hand-carry it, and then power up again when needed? Or would that be too OP, and unbalance things too much in my favour?

RAW, no you cannot. You can summon it and then you have to summon it again.

This is annoying not just because of the spell slot but because it means possibly that your first turn of combat has to be spent activating the cannon instead of having it around all the time.

Worse, it means that the Short Rest that is beneficial to everyone else in the party is actively detrimental to the Artillerist, costing them a spell slot.

By contrast, the steel defender and homunculus stay up indefinitely, until they run out of hit points.

I am not sure why this choice was made, honestly. If you are playing at your own table, I don't think it would be particularly OP to just let you keep the cannon up all the time, stored in a Sleep mode. The cannon is already decently costly to use - your bonus action on every turn. It means you don't have a bonus action for any other feature, or for downing a potion, or any of the other things that say a Battle Smith or Armorer with Extra Attack can do. You can't even have the cannon default to say Protector mode as a default, the way you can set the Steel Defender or Homunculus to dodge. 

Quote from FoolishMortal18588 >>

RAW, no you cannot. You can summon it and then you have to summon it again.

This is annoying not just because of the spell slot but because it means possibly that your first turn of combat has to be spent activating the cannon instead of having it around all the time.

Worse, it means that the Short Rest that is beneficial to everyone else in the party is actively detrimental to the Artillerist, costing them a spell slot.

By contrast, the steel defender and homunculus stay up indefinitely, until they run out of hit points.

I am not sure why this choice was made, honestly. If you are playing at your own table, I don't think it would be particularly OP to just let you keep the cannon up all the time, stored in a Sleep mode. The cannon is already decently costly to use - your bonus action on every turn. It means you don't have a bonus action for any other feature, or for downing a potion, or any of the other things that say a Battle Smith or Armorer with Extra Attack can do. You can't even have the cannon default to say Protector mode as a default, the way you can set the Steel Defender or Homunculus to dodge. 

Exactly! I'll have to discuss with my DM whether we can make a little homebrew change. We're already homebrewing a bunch of other things, including "wild magic" power surges that I can trigger if I roll a crit. I'm fine with it taking an action or magic action to deploy the turret if it means I can keep it all day. 

That reminds me; in dndbeyond's character sheet it displays a "Special" mode for the Cannon, separate from the regular three modes, with 15 uses. Anyone know what this is? Homebrew? Future upgrade/change?

Quote from FoolishMortal18588 >>

This is annoying not just because of the spell slot but because it means possibly that your first turn of combat has to be spent activating the cannon instead of having it around all the time.

Because it's a full hour, you often summon it a little bit before you expect combat. And if you are doing some sort room-to-room dungeon crawl, you can probably get a few fights into a single hour of character time.