You might need to dump the ROM from a bootleg that already has a batteryless patch applied to it. Another issue you'll face is Pokemon games use dual-banking, and save two copies of the save in 1Mbit of save space. Multiboot carts only have 512Kbit of space, so hence why Pokemon ROMs never save right on them. Honestly, bootlegs are fantastic for everything except Pokemon. Spend good money on a GBA Flash cart that has RTC functionality for your Pokemon games, and then you can use bootlegs for everything else.
Feel free to jump into Bennvenn's Discord server, as we're very helpful and knowledgeable about this stuff, and you'll likely get faster replies there too.