Unzip it, then either rename and put it where your save files are stored, or in VisualBoyAdvance you can simply go to File->Import->Battery File. Make sure your "save type is set to Flash 128k (Options -> Emulator -> Save Type).
Character Profile 38/38 Story Line 51/51 Time Attack Unlocked All Grand Prix modes unlocked and completed. All cars unlocked (including Red Bull, Blue Falcon GP, and Hyper Death Anchor) Survival Tour 39/36 Survival Challenge 39/36 Survival Battle 01/36 Survival Violence 00/36
I think that's everything that's unlockable, if I missed something please tell me.