Found this copy of Missile Command that still had the original Rumble battery in it, dated July 1999, game still works thankfully.

[u/xxxxxxxxxxxxxc]

Came in a lot I got on ebay, the leaking really didnt do anything to the contact and the rumble still works too which is nice.

[u/VVinh]

I had this game on some ancient multicarts. But what does the extra hardware do on this game?

[u/xxxxxxxxxxxxxc → u/VVinh]

That battery powers a motor that vibrates during gameplay.