Well, it's good to see someone else interested in this subject!
I've been giving up on trying for a while so here's a wrap-up for those who were still trying:
Our previous attempt was to find a non-volatile drop-off replacement for the SRAM chip on genuine Pokémon carts so that the carts can save without batteries.
(Sorry aldighieri, your carts were repro carts, which were not official Pokémon carts and thus not related to the discussion. Official Pokémon carts don't have glob tops.)
Every Game Boy cart has a chip called MBC. In Pokémon carts, there are 4 different types of MBC:
- MBC1: the oldest MBC which could be found on early titles
- MBC3: the MBC introduced between MBC1 and MBC5; in addition, MBC3 was required for most games with real-time clock (RTC) features
- MBC5: the latest MBC which could be found on titles released near the end of GBC's lifecycle
- MBC30: a special type of MBC found only on Japanese Crystal for RTC and large RAM support
A table of which Pokémon cart comes with which MBC is shown below:
Code:
R/G/B Yellow G/S Crystal
Japanese MBC1 (MBC3) (MBC3) [MBC30]
English (MBC3) MBC5 (MBC3) (MBC3)
European MBC5 MBC5 (MBC3) (MBC3)
The problem we had run into was that while there exist some known FRAM chips (FM1808-70, FM1808B and FM18W08) which in theory could be the replacements we're looking for, our installation attempts showed that they only work on MBC1 and MBC5 carts, and will result in graphic glitches and save failures on MBC3 carts.
Since most of the Gen II games come with MBC3, this means that we have yet to find a replacement for the Gen II games. We'll either have to find other replacements or install additional circuits instead of just a drop-off.
(Note: Japanese Crystal is out of the question since its RAM was 4x larger than other games and no replacements are available.)
Hope this explains the situation we're in.