I bought all the GBA FF games off eBay and only received counterfeit ones :-/ At least the ones I got don't have batteries in them. Saving makes the games freeze for a small time but other than that they are working.

Completed the FF V GBA counterfeit on a DS lite. Ended up playing through the DS versions of III and IV, also off eBay, which do not seem to be fakes fortunately.