I have to go on a long-ish car trip and will be using Maemo Mapper on my N810 as a nav unit. I have a 2nd battery with me. But I want to conserve battery life as much as possible.

Which would save batter life more: using the onboard GPS or an external GPS via Bluetooth?

My gut says that the onboard GPS will use less power than the Bluetooth transmitter. But...does anyone have experience or even a guess?

Thanks.

Pick up a DC adaptor.

No experience, but I'd bet on the BT, since you asked for guesses.

Get an inverter, and use the AC adapter. I have a USB cable ordered, which is supposed to fit the Nokia for charging from USB chargers, but I haven't received it, so I can't say if it actually works. I have USB chargers for both AC and DC, the latter plugs into the cigarette lighter port and gives a USB port on the back, for charging standard 5VDC devices.

BT, provided it does NOT send a lot of extra traffic (extra NMEA sentences) and works at 1Hz and not 5Hz, as the mapping sofware tends to update faster too.

Grab yourself a CA-100 cigarette lighter adapter and you won't have to worry about the power...Moreover, as far as I can tell, when the unit is plugged in, you can set the auto-dimming function OFF...Otherwise that is a real pain in the butt....You can't lock the screen, or you can't turn the screen back on...but you can't use full-screen because unless you touch the screen on the far left side, it turns off auto-centering. ...And recovering from that is somewhat dangerous if you are driving...

Geoff

The cigarette adaptor is a much better method. El Cheapo DC inverters (anything below about $120) are incredibly noisy and failure prone (not to mention potential firehazards <_<).

I don't agree. I've been using inverters for years, and haven't noticed any noise problems at all. The AC is being converted immediately back to DC, so there is no noise problem. A DC adapter works, but some people need more outlets. I run 4 or 5 devices off my inverter many times, with no problems. I have an mp3 player that only has an AC power supply, and I can't find a DC adapter for it, as well as my cell phone, for which I just don't want to pay for a DC adapter. Inverters work well, and the stories of noise and touchpad jumping are just stories. The device only knows it's getting the proper DC voltage, whether it originated in the wall or from an inverter. Cheap DC adapters are just as dangerous as inverters, and it can be hard to find one with the exact voltage you need, as well as the proper amperage. With an inverter, you know you're getting the proper voltage.