I have seen something like this:
(http://rot47.net/_s/upload/2014/06/16/6bb8831e42e757f6d45b0ab861cc4e73.jpg.jpg)
http://rot47.net/share-picture/8o (http://rot47.net/share-picture/8o)
are those batteries used to store game progress? where can I get cartridges like these?
Yup, they were used to store savefiles.
I guess you can find pcbs with battery slots in rpgs like Mother or Dragon Quest. There should be a list of battery-save games somewhere.
The first Dragon Quest actually uses passwords instead of saving (Dragon Warrior however uses battery backup).
The only list I know is if you search Bootgod's database. I searched for all games with battery: http://bootgod.dyndns.org:7777/search.php?keywords=&battery=Yes&offset=0&field=2&order=asc
Note that Bootgod's database doesn't contain all games yet.
Sachen's Millionaire 2 contains a battery.
Why are you wanting pcbs with batteries?
some pirate games like Diablo II and W.o.W have batteries to store savegames too.