Conky always tries to read the battery info from the sysfs paths first:
/sys/class/power_supply/bq27200-0/uevent
If that doesn't work, it falls back to dbus, which gets it from bme.

I don't like the bme ones because they don't update when the n900 is charging. I also don't like them because the source is closed and we have no idea what it's doing or if it's really more accurate. I guess the only argument for why it's accurate is it will shut your phone off when it thinks the battery is dead.
If you really don't like the bq27x00 driver's values, you can use the .conf file to obtain the battery info with $execi, just search this forum, there's about 20 examples of how to do it.