I'm converting my games to NVRAM presently, so the answer soon will change to never

But presently, with remote holders, once a year.

I find the 'old' ones are great for remote controls, kids toys, etc. Probably would be good for more like 4-5 years if you didn't worry about audits, customizations etc in remote holders.

The batteries in most pins simply provide battery backup to the RAM chip contents. The RAM contains things like high scores, audits, game customizations like free play, custom messages, etc.

NVRAM doesn't require the battery backup. It maintains the information without an external battery. It's not as cheap as 3 AA's in a homemade remote battery pack, and it requires you replace the RAM chip from your MPU board with a socket, if your game doesn't already come with a socket. Data East games, for example, tend to have socketed RAM. WPC games don't. The traces running to the RAM on WPC MPUs are small and delicate, so this is NOT the board to learn to solder on. But, I like the 'set it and forget' it idea. The only one of my machines I don't intend to install NVRAM on is Twilight Zone.

Why? The NVRAM doesn't keep the RTC (real time clock) accurate. Since TZ sets the time of the clock on the playfield to the CPU board, this is the one game I own where the clock's accuracy matters to me. For TZ, I'll stick with a remote holder.

It might also be an issue if you have a game with Midnight Madness mode.

I didn't go with the Pinforge solution; but it looks like a good alternative, and Todd @ Big Daddy sells them.

http://www.bigdaddy-enterprises.com/ProductPages/pinforge.html

I was able to track down a few DIP parts that didn't require the adapter board.

Those parts have pretty much dried up at this point, so the surface mount parts with adapter boards are pretty much your only choice.

The function is the same; the pinforge ones will work just fine