Smartphones aren't really phones. They are small personal computers that you can carry around with you. They just happen to also make phone calls -- but that's not what most people use them for. Yes, these tiny computers are awesome and useful -- but there is a downside. The battery life is terrible. The only way I can make it through a day without an extra charge is to just not use the phone.
Possibly the two things people want in a new phone are better battery life and a better camera. But how could the battery life of a phone get better? There are only a few things that could change. Let me go over the options.
Bigger Batteries
Suppose your phone runs for 5 hours if you are continuously using it. How could you make it run for a longer time? You could put in a bigger capacity battery. Before the iPhone 6, all the previous iPhones had about a 1500 mAh lithium-ion battery. What is "mAh"? This is short for milli-Amp hours. So a 1 mAh battery could produce 1 milliamp of current for 1 hour. Yes, it's a measure of the energy stored in the battery. You can find out exactly how much energy if you know the battery voltage. For the iPhone 5s, it has a 1570 mAh battery with a voltage of 3.8 Volts. If you know the voltage and the current then the power and energy would be:
If I know the current in milliamps and the time in hours, I can use this to get the following expression for the energy in a battery (in Joules). Here is how you would do that calculation for the energy in the iPhone 5s battery.
Ok, that seems like a large amount of energy but maybe it's not enough (well, it's not enough for me). What if you put a bigger battery in the phone? Wouldn't a 3,000 mAh battery last about twice as long? Yes, I think it probably would. However, there's a problem. If you use the same kind of battery it would be about twice as large and twice as heavy. It might not be exactly twice the size since a larger battery can have a smaller percent of size devoted to the outer cover and other required components -- but you get the idea.
There is one way to deal with a bigger battery that doesn't make everyone hate the phone -- make a bigger phone. If you have a larger phone, some things don't change size -- like the processor and the camera. Sure, the screen gets bigger (and uses more energy) but you can still put a larger battery in there. Look at the iPads. They are much larger than an iPhone and they seem to have fairly decent battery life. Maybe the iPhone 6 Plus will have super awesome battery life (Apple claims it will be better). Just to be safe, Apple should send me one so I can test it.
Higher Battery Energy Density
Just about all phones use lithium-ion battery. These have about 4.32 MJ/L (mega Joules per liter). Yes, energy density is the energy stored per unit volume. I'm not sure why, but it seems that a common symbol for energy density is u and is defined as:
It's just like mass density except that it's for energy. There is also the specific energy. This tells you the energy per unit mass -- but I'm not too concerned about the mass of my phone (but volume is important).
Where could you find the energy densities for different storage solutions? Of course Wikipedia has you covered. Here are some interesting energy densities:
- Gasoline = 32.4 MJ/L
- Lithium-ion = 0.9-2.63 MJ/L
- Lead Acid Battery = 0.34 MJ/L
- Sandwich = 10.13 MJ/L (whoever added this to the Wikipedia page is a genius)
- Antimatter = 9.266 x 10104 MJ/L
If you want to keep your phone battery the same size but increase the energy storage, you will need to find something with a higher energy density. Right now, Lithium-ion is the best we can do for a battery. It seems safe to bet that in the near future humans could find something in the 5 MJ/L range for a battery, but that will still just bump the battery life up by a factor of 2. Twice the battery life would be good, but I would like something even more impressive.
A phone that runs on sandwiches would last about 5 times as long as a Lithium-ion powered phone. Of course you would have a tiny little sandwich in your phone and you would need a tiny little stomach to go with it. On the downside, you would have to take your phone to the bathroom at least once a day or deal with it pooping in your pocket (that would be awkward). Oh, don't forget to feed your phone. It would probably take less time to feed a phone than it would to recharge a battery.
What about an antimatter powered phone? If you had the same size antimatter battery as in your current phone, it would last about 10100 years. Just for comparison, the Universe is most likely 14 billion (14 x 109) years old. Now, don't get all excited. There is still the problem of taking antimatter annihilation energy and turning it into electricity to run your phone. It would either require much more space or the radiation might kill you. Still, the phone should at least run until Apple announces the iPhone 22sd Plus in the year 2034.
More Efficient Phones
What if you keep the phone the same size with the same battery? Can you still make the phone last longer? Yes. You could make a phone that uses less energy. Maybe the display is more efficient or maybe the processor is better -- but either way if a phone uses less energy it will last longer. I think this is essentially what has happened with some of the newer laptops that have a 10 hour battery life. The batteries in these laptops aren't really that much bigger but the processors are more efficient.
Recharging While You Go
What if the phone was recharging all the time while you were using it? Of course you would need some type of external power source -- but maybe that would work. Here are some options.
Recharging by Typing. What if each time you pushed on the phone to type, it turned that into energy that charged the phone? It seems like a great idea, but I looked at this before -- it wouldn't work. You just don't get enough energy from each "push" to make this method work.
Solar Charging. If your phone had a solar panel all over the case, it could charge from the sunlight. In a previous post, I looked at the "best case" for solar charging. If you left the phone in direct sunlight (and facing the Sun), you could charge it in 4 hours. That's the best case. Realistically, this could extend the battery life a little bit.
Charging with Sound. Think of sound waves as oscillations in air pressure (since that's what they actually are). These changes in air pressure could push on the phone in a very similar way that your finger pushes on the phone while typing. Are you surprised that I already looked at this charging method? The best case scenario for charging by sound would take over 100 days to charge a phone using conversation level noise. Unless you plan on living at a construction site or at a rock concert, this method is useless.
Kinetic Charging. There are some mechanical watches that don't need to be powered through winding. Instead there is a mass on a spring inside the watch. Just through the process of wearing the watch, this mass-spring gets moved around to store energy in the watch. You could do something similar for electric watches. A magnet moving through a coil of wire can also generate an electric current. Could this work in a phone? I'm going to say "no." I looked at this same idea for smart watches and it's just not going to produce enough energy to make a difference.
Wireless Charging. Wireless charging is already "a thing." In fact, the Apple Watch will use wireless charging. It sounds cool, but it's not going to be that helpful for smartphones. I have a nice summary of the physics involved in wireless charging (inductive charging) -- but the key point is that you have to have the device and the charger close to each other. It's not a long range thing. Wireless charging could make a big impact though. Since it means you don't need a charging cable, you could have ubiquitous charging. You can put your phone down on the table or in your car and BOOM -- it's charging. That would be nice.
The Future of Phone Batteries
In the end, I think the best solution is a mixture. If we can make higher energy density batteries (which we can) and we can make more efficient processor (which we can), the combination of these two should make a phone that at leasts last through the day. I welcome that phone.
