Wifi drain is a myth in the sense that people think the radio drains it. At 10 mW, it drains about the size of an LED. It is not a myth in the sense that using it requires the CPU to be up, the math to keep up WPA/2 is quite intense (the major drain in WiFi is the computation). Using wifi to transfer requires several things to be up, network layer, TCP/IP included, driver, daemons that watch on/off, periodic searcing for handover on wifi arrays, etc.

As for BT, same deal, mostly. Lower requirements, but still.

As for our car battery friend, I'd recommens wired headsets, that could cut your usage in half in a best case scenario, and get you a noticeable 20-25 percent in worst case (these are guesses).

Wifi is cooler if the AP supports sleep, but if you trickle data through it (streaming) versus bursts (HTTP), it useless. Also, power save shoukd be maximumin N900 for this to work. Also, open auth and a mac filter is better power but poor security versus WEP/WPA.

Playing from internal memory via wired is gonna save. Pick a minimalist player, like mplayer versus Instinctiv (I have no idea how much each eats, I just picked minimal versus cool).

And remember, the biggest drains in N900 are screen on full, CPU, GPU, WiFi, GPS, BT, roughly in that order. Depends on usage.

For me, I have more that 50 percent increrase in life by browsing at 2/5 light that 4/5 pips in the light setting. More ambient light helps.

So, watch CPU usage in player, get wired headsets, play from eMMC, you should see an increase. As for streaming via WiFi, not much I can recommend. It just plain drains.

And, if all you do is play audio, lower CPU clock, it saves when in low usage. For me, it doesn't work, when I fire it up the CPU shoots as I do intensive stuff. The quicker I'm done, the better. I had better battery at high CPU clock.

Have fun.