Are there any cheats for sonic battle for the gba?

yes there is.

To unlock Amy Combo card enter alogK as a passWord in Emerl's story line at the Sonic Team Building.

To unlock Chaos Combo card enter EkiTa as a passWord in Emerl's story line at the Sonic Team Building.

To unlock Cream Combo card enter ZAhan as a passWord in Emerl's story line at the Sonic Team Building.

To unlock E-102 combo card enter tSueT as a passWord in Emerl's story line at the Sonic Team Building.

To unlock Knuckles Combo card enter yU3Da as a passWord in Emerl's story line at the Sonic Team Building.

To unlock Rouge Combo card enter AhnVo as a passWord in Emerl's story line at the Sonic Team Building.

To unlock Shadow Combo card enter ArmIa as a passWord in Emerl's story line at the Sonic Team Building.

To unlock Sonic Combo card enter 75619 as a passWord in Emerl's story line at the Sonic Team Building.

To unlock Tails Combo card enter OTrOI as a passWord in Emerl's story line at the Sonic Team Building.