Hello, all. Having never opened an SNES cart, I was wondering a bit about the SNES battery:

-Is it a replaceable battery that can be bought at a retail store? I once heard that NES carts have watch batteries installed, which are easy to replace.
-How long are they expected to last? I'd imagine 15-20 years.
-How does one go about opening the SNES cart?
-Are there any available guides online that deal with this (preferably with pictures)?

Thanks, all. Have a good day.