I was told anything using removable flash memory has much worse battery life than other type flash carts.
I don't know how to make it any more clear to you. I own an EZ4 and use it daily for up to 9 hours at a time and still do not manage to empty a fully charged DS battery. I own a DS not a DS lite, Nintendo says that the battery should last about 10 hours depending on what software you are running on it... I can get 9 out of it at least, probably more if I worked more hours. I haven't actualy tested the 10 hour limit because:
1) While I have plenty of time to play w/ my DS at work, some times I do have to turn it off or put it to sleep.
2) I can't be bothered to leave my DS on and open till the battery fails and time it.
3) When I get home I plug my DS in so that it will be charged for my next day at "work".
Own a Gameshark, Action Replay, PassMe, etc? Those will tank a full DS battery in 3-4 hours. An EZ4 has no more effect as far as I can tell, w/o serious testing I can't be bothered to do, on the DS' battery then "normal" use. Keep in mind I also own an EZ2 and EZ3, and w/ regular use I can find NO difference in battery usage between the 3 carts. As far as SC and M3 I can't say beyond what I've read: M3 = minimal difference in life, SC = battery draining pig iron.
Given my results, do you use your DS for more then 9 hours at a time w/o plugging it in at some point?