You need to load the multi-out version of Battery 3 to do that, not the stereo out version.
There is only one version of Battery, Tarekith.
And you don't need to use the "External Instrument" of Live 7 to route Battery's outputs to specific different tracks. Make sure you are using the latest Update 3.0.3 (12-18-2007). Also when changing Battery's outputs (like number of outputs or stereo-mono changes) you need to unload and reload Battery twice
for the changes to be working properly.
Just set the "Audio From" settings of your target audio tracks to the midi track that the Battery instance is running from. Then change the setting right below that from "Post Mixer" to the Battery output you like to route from. Works like a charm!
If you are using Live 7 though, you might prefer using a Drum Rack and use the ability to fold/unfold the Battery tracks for better overview. Look here how it's done:
http://www.ableton.com/forum/viewtopic. ... ht=battery
There is one main restriction which I thought to be Battery's fault, but after the latest Update it seems to be a Live issue. You can only select/use 15 additional channels beside the main stereo channel in Live even when Battery offers upto 30 Mono channels.