And the cost?
This is one of the easiest hacks to do, and it'll save you about $40. I picked up two A23 12-volt batteries for less than $2.
After splitting the case with a screwdriver and peeling it back, what you'll find inside are eight 1.5-volt button cell batteries.
I found the matching battery for $4.99 at an electronics store. I was able to power up these 6 devices with the batteries I hacked from the 12-volt battery! And I saved about $40! Cheap and easy with a big payoff: the 12-volt battery hack. (Kipkay)
Here is the short demo video: