I didn't think LeafGreen-and Firered, had an internal battery or at least an issue with it, most of the complaints about the batteries come from Ruby and Sapphire, you should probably ask someone in the club though (I don't usually hunt on the GBA games, but I'm slowly getting into it) Good luck with the squirtle though, I'm actually going to go for one too.
Dry Battery means you can't sr for shinies on that game, I'm assuming you're talking about the internal battery, right? I think however that you can still hunt for them in the wild but I'm not completely sure. Why?
And I got bored and read something you wrote. Do you mean to say that you got a SR Shiny Suicune and didn't save it? Cause if you meant that than you are not gonna be able to get it back that easily, sorry to say.
Here are some tips:
-save right before you "talk" to Cresselia at Fullmoon Island
-Exit the island and fly to Sandgem town right away (your flyer should be in the first spot of your party)
-Go back and forth between Sandgem town and route 202 until Cresselia is in route 202 (you can see the location of roamers on one of the Poketech apps)
-apply a repel if you don't want to be annoyed with Starly's while trying to find Cresselia
-Encounter it, then SR if it's not shiny
You don't have to go to Sandgem town, but it probably works best. These SRs take a while, so you may have to be very patient. I hope these help and Good Luck