I'm pasting this from a reddit post, sorry to cross post, but no-one knew on reddit:
I bought a flashcart of amazon. It all works fine apart from the save game functionality.
I have patched the games using the (hideous) windows application and I have ensured that the saver checkbox is checked. So in a game, I should be able to press L+R+A+Select to save the sram to sd, but nothing happens (on either of my SP or DS). The soft reset key combo works fine, just not the save.
I tried a diagnostics check (hold L+R when booting the cart). The card's firmware is current (1.85). There is an SRAM error:
Test SRAM SRAM error: 0105
I am not sure how this relates to the issue, but by googling, it seems that the same error can be anything from ineffectual to rendering the cart unusable. Is the internal battery dead perhaps (although IIRC it is rechargable)?
I have tried the manual save technique too; using the soft reset key combo and then saving the game to sd using the saver tab on the main flashcart interface. Whilst this at first appears to work, after I load the game again, the save is lost.