I've tried it (on a N3DSXL) and you can. There's a little tab there in the compartment to prevent exactly this, but you can cut it off and it works just fine. The capacity is lower so expect less battery life (probably same as a N2DSXL which actually uses the same battery as the small systems), but it's cheaper than an XL battery and might be useful in a pinch if you only have a small one. Note that the battery needs to be held with something or else it'll move around, probably like tape or something.
