I'm pretty sure that minger was referring to the DS battery, not the SRAM battery in the 3-in-1. I haven't done any real testing, but the 3-in-1 doesn't seem to drain the DS battery any faster than the R4/M3 Simply.
The 3-in-1's SRAM battery is rechargeable, and it should charge wile you play the DS with the 3-in-1 inserted.