I’m pretty amazed at the latest gadgets coming out from the R&D departments of consumer electronics companies, such as Nokia and Apple – the N95 is a super-duper, do-it-all, cellphone (sorry, Nokia wants us to call it a ‘multimedia computer’), featuring multiple bands, HSDPA 3G (Europe only), WiFi, GPS, and a 5Mpixel camera, apart from a wide array of software tools for blogging, posting pictures online, navigation and more. What price does this device pay? A meager 950mAh battery, which lasts less than a day under normal use, considering ‘normal’ as actually using the functionality it offers. I guess you can get more if you turn off the GPS, WiFi, don’t use the camera, and make almost no calls…but then what good are all the bells & whistles for?
The iPhone case is even more interesting, as the device has not been released yet, but Apple has already reported an increase in battery life with respect to the initial quoted value. The iPhone will have 8 hours of talk time, and some 250 hours of standby time, with 5 hours of video and 24 hours of audio playback. Apple’s stock has jumped $3 since the announcement, something that will make losers in the fake email crash happy.
Let’s try to make a simple breakdown of power consumptions, and see if manufacturers are being overly optimistic.
WiFi
One of the biggest power drains, as there is no built-in power management into the WiFi protocol, contrary to GSM and 3G. When transmitting over GSM, a phone makes calculations from data received from the network and its own measurements in order to adjust RF power to the minimum required to reach the cell’s base station. Thus, in areas of good coverage, a phone can be consuming far less power than in rural areas with more spotty coverage. While on a 3G network, the rate of adjustment is even higher. WiFi chipsets in mobile phones have basically two settings, “high” and “low”. Most times, unless you are sitting right next to the access point, and without any major interference, the setting the phone will use is “high”.
Assuming that the WiFi chipset used by the Nokia N95 and the iPhone use little power, for example, by fitting the Nanoradio solution, the power consumption would stand at 130mA in transmit mode, 53mA in receive mode, and 50uA in standby mode. Assuming we are receiving 80% of the time, for example, by browsing the web, the average consumption would stand at around 68mAh. The N95’s battery would last 13 hours, if it had to power the WiFi chipset alone.
GPS
Even though GPS technology has advanced a lot since the early days, GPS chipsets can draw upwards of 80mA. Special trickle-power configurations (which also impact performance) can reduce this to 50mA or so. Thus, the N95’s battery could power the GPS for around 19 hours.
Processor
The Nokia N95 features an ARM11-based Texas Instruments OMAP2420 running at 330MHz, featuring 2D/3D video acceleration on top of whopping performance. What does this mean in electrical power terms? Even though this processor features SmartReflex technology, which reduces static leak currents (a good technical overview is available here [pdf]), the net current drawn is around 30mA. The N95 battery could power the main processor for around 32 hours.
Display
The display on the N95 is very good, beautiful, 16M colors, 240×320 pixel resolution. It is also power hungry, taking around 30mA, thus, the battery could also power the display for around 32 hours.
Phone
Assuming that you talk 5% of the time on the phone, the average power consumption by the phone subsytem alone would stand around 20mA, resulting in a battery life of 47 hours.
Adding things up
So far, we have seen how much the battery could keep running each individual system on the phone, but adding things up, we have a power consumption of about 100mA (taking into account that we are not using everything at once, I halved the figures). This results in around 9.5 hours of operation, more or less an average day. This ties in with most users’ experiences, as shown in many reviews done so far on the N95.
The iPhone, being much thinner, wider and taller than the N95, probably won’t have that much larger battery capacity – why does Apple give the figures they do, I can only blame on the marketing department. This is not as uncommon as it seems, R&D provides a set of carefully calculated and actually measured results, then the marketing guys take them and multiply them by two. Anyone who has used a modern, high-end phone or PDA, will attest to the fact that quoted battery life figures differ from reality by far. I don’t know of many companies that can raise their stock $3 by simply increasing the value of the battery life in one of their products – this shows how much hype there is around the iPhone (of which I’ll most definitely get one…they are soooo sexy!).