I was reading on some used game sites that sell old cartridges like SNES, Sega Genesis, etc that they clean the cartridges and replace the game save battery.
I'm not too sure what this means and there isn't much info to find.
Does anyone know what is inside the cartridges? Do you clean them? Is there some sort of battery? What tools are needed? How easy is it to perform maintenance?
I'm mostly concerned about giving them a clean to sustain their life and to be able to save games in certain releases. Don't mind doing the small things myself, if needed I can bring something to one of these restoration/video game places.
There is indeed a battery inside old cartridges. I have never needed to replace any of mine, but I have read about the batteries wearing out and needing to be replaced. If the cartridge is still holding saved games, you don't need to do anything, but if the saved games are not being kept, you will need to replace the battery.
Many of the old NES / SNES / SEGA game cartridges contain battery backed CMOS. Basically the same thing your computer use's to keep it's BIOS configuration is used to keep a small portion of memory alive on the cartridge. These wear out over time, typically in 5~10 years depending on quality and how much memory it's keeping alive.
I replaced the battery in a WarSong (http://en.wikipedia.org/wiki/Warsong) cartridge once. It was a typical CR2032 and very easy to replace. Sometimes the batteries are soldered in, so you either have to heat the existing solder until it loosens (recommended) or cut the battery off along with a small piece of the conductor (not recommended). You don't necessarily have to resolder the new battery in, but if you drop the cartridge afterwards, the connection might break for a split second, and you will lose the saves, so get a soldering iron and practice.