Even with the extended battery life of the iPhone 4, the battery seems to drain away very quickly when you are making use of your GPS system. That is not just an optical illusion; the use of your GPS turn-by-turn navigation system goes through some serious battery. I regularly do long trips, often in the 1200-1400 mile range, all in one go. There is no way that a single charge of the battery will last that long while running the GPS.
Even for much shorter trips, all GPS systems tend to use a lot of battery. That’s because they must energize the GPS chip, do a lot of memory fetches to keep the display current, and most have a very busy display and use spoken driving commands. All of those things use a lot of battery, so your charge rapidly disappears. Until recently, I used the TomTom GPS system on my phone. Since I got it when I had a 3G version iPhone, I also needed the TomTom car kit because the 3G GPS chip internal to the iPhone was not very good. The car kit both boosted the GPS signal and charged the phone.
Still, on a long drive, even constant charging would not always keep up with the battery drain. The iPhone 4G does not need the signal boost, which is a good thing since using the car kit is pretty problematic with the 4G anyway, something which TomTom has never addressed, as far as I know, making my $120 car kit a fairly light and useless boat anchor. Taken together with the really huge and burdensome (and sometimes bungled) updates for the software, and a general feeling that I had been screwed by spending more for the TomTom app and the charger than my phone, I have switched apps.
I am now using GPS Drive by MotionX, which seems a bit easier on the battery than TomTom. The download of updates is a lot faster, too, since the maps are not on the phone but on the MotionX server. That causes some battery drain as well, since you may have to download new maps from the internet once in a while, but on the whole my new system tends to use less battery than my old one.
Plugged into a charger, the phone seems to hold a charge even when I play my iPod app music through my car’s speakers (see here for the accessories I use).Even at that, I hedge my bets by some modifications of usage. For example, you don’t need a lot of GPS help to stay on I-70 between Indianapolis and Columbus, so I tend to turn the GPS off entirely on legs like that. Even around town, I find that the voice commands from the MotionX system are good enough that I can run it in the background with the display off.
All in all, I’m much happier with the iPhone 4 and MotionX, which is basically a free app, than I was with 3G with TomTom’s app and car kit. MotionX is even bright enough to know the best route through St. Louis, something TomTom could not manage. The only feature I miss from the TomTom system is the lane highlighting at complex highway intersections, and that is coming soon to MotionX.
All in all, I wish that I had not thrown away my $220 on the TomTom system in the first place, and come out of the box with MotionX. Whatever you use, though, you will probably benefit from turning your GPS system off when not needed, and keeping it in the background with the display off most of the rest of the time.