All you wanted to know about batteries but were afraid to ask: March 2015

Friday, March 27, 2015

58. SAMSUNG, BE HONEST IN YOUR MARKETING CLAIMS

Samsung announced in September 2014 its GALAXY Note 4, a giant but elegant 6-in screen smartphone with a specified battery capacity of 3,220 mAh. It also made a bold claim that it charges the smartphone to 50% in 30 minutes. The marketing snippet below comes straight from their website. So, how honest is Samsung in their marketing claim of fast charging? Let's find out.

We set out to test the Note 4 in our lab. We conducted charging cycles, measured the charging current into the battery as well as the battery capacity and the corresponding state of charge (the percentage the user reads in the top part of phone screen). The measurements were done with the accompanied Samsung fast charging adapter, with all wireless functions turned off, GPS and location services turned off, and the display turned off. These ensure that the current provided by the AC adaptor is entirely used for charging the battery and no other function. The smartphone was completely discharged before initiating the charging. The battery was deemed fully charged (100%) when the charging current dropped below C/20, or 1/20th of the rated capacity; this is equivalent to the charging current dropping to 3,220/20 = 160 mA. This metric is a commonly used standard of full charge in the lithium-ion industry. What were the measured results?

First, let's look at measured battery capacity. We measured a full charge capacity of 3,185 mAh, or 99% of the specified capacity. This is as accurate as one can measure it. Kudos to Samsung for being honest about the capacity...but Samsung's marketing and engineering departments decided to stretch the truth in their claims on charge time and state of charge. Let's examine these next.

Measured charging current (red) and corresponding state of charge (purple) for the tested Note 4.

The next chart shows the state of charge (as a percentage of full capacity) on the left hand side (corresponding to the curve in purple), and the charging current (in mA) on the right hand side (corresponding to the curve in red). The state of charge is what the Samsung fuel gauge software reports at the top of your screen.

The first observation we make is that the fuel gauge reports 50% in 37 minutes, not 30 minutes as claimed by Samsung. Ok, Samsung, is 37 minutes equal to "about 30 minutes"? Perhaps if these extra 7 minutes don't mean much to a patient consumer, but I can't see how an end-user in a rush to catch their next connecting flight won't notice these precious seven minutes.

The second observation is where the phone reports 100% full charge, or the total charge time. Focus your eye on the purple curve right about 90 minutes of charging time. Right there, the fuel gauge almost instantly jumps from 94% to 100%. In other words, the software in the Note 4 decides that 94% is full enough to "round it up" to 100%. The actual full charge time, i.e., when the battery does reach its specified 3,220 mAh is 120 minutes, but the smartphone tells you (incorrectly) that it is fully charged a whole 30-minutes earlier! That's nearly 200 mAh of capacity, or about 1 hour of usage, that you have been cheated. Ouch! Shame on you Samsung!

The third observation is that Samsung is using straight CCCV charging. Judging from these charts, their charge rate is approximately 0.75C, only a hair faster than the iPhone 6 or 6Plus which clock in at 0.7C. So, are we now claiming fast charging at these low levels? Why can't you promise the end users 1C or above, and then proudly advertise fast charging.

Please, please, be honest about your marketing claims, Samsung. Consumers are no dummies...they will eventually realize that you are stretching the truth in your marketing claims.

Sunday, March 15, 2015

57. UNDERSTANDING POWER USAGE IN A SMARTPHONE

You are shopping for a new smartphone and you are trying to understand how long the battery will last. But you can't seem to get a straight answer. Apple says the iPhone 6 will last up to 14 hours of talk time on 3G but you are really not going to have your iPhone glued to your ear for 14 hours. Motorola is more subtle about its claims: up to 24 hours of mixed use. Other manufacturers follow the same strategy of being vague about their claims with the operative word being "up to."

The reason nobody wants to commit to battery life is you, the user and consumer. We each use our mobile device differently. Some of us use the device as a phone more frequently, others use apps more intensively. Some of us turn off plenty of background services such as data refresh, whereas others want their GPS operating with as many apps that request it. This creates an infinite number of combinations of use, and hence makes the "average user" profile somewhat of an oxymoron. This blog will shed some insight onto what components and features in your mobile device are power hungry and what you can do to limit the times that these power-hungry features are allowed to access your limited battery capacity.

The most power intensive components in a smartphone are the display, the processor (or CPU), the various radio functions (and there are several radios in your smartphones), the location services, in particular the GPS system, and the memory, in particular, writing into memory. Naturally, they are not equal in their power consumption, so we will attempt to put some power figures for each of them as well as rank them in terms of their power needs.

1. Displays: The display and its associated electronics (backlight, touch screen controller, graphics processor) are by far the most power hungry component in your mobile device. Modern smartphones have some pretty impressive displays but the more pixels they pack, the more power they consume. The Galaxy S6 has a spectacular 2560 x 1440-pixel Quad HD display but I can imagine it will be a serious power hog. Naturally, Samsung will not share these power figures with the public but one can estimate from various publications and lab tests these power levels to be about 1,000 mW for a standard 5-in HD display, and rising to 1,500 mW for the quad HD screens. A battery with a capacity of 2,600 mAh or equivalently 10,000 mWh, this translates to about 6 - 8 hours of active screen time. A couple of years back, these power levels were nearly half what they are now because the screens were smaller and were at most 720p. Tidbit #1: If you must have a large screen, reduce the backlight screen intensity. Backlights can consume several hundred milliwatts.

2. Processor: A an octa-core running at 2.4 GHz all the time will most likely cause a thermal shutdown of the smartphone quite rapidly. A processor running at full steam will consume 3,000 mW at its peak -- and generate a lot of heat. Fortunately, these peak events are short-lived and may be infrequent depending on your usage. But still, applications that are processor intensive will invoke that processor horsepower more often than you desire and deplete your battery. Rogue applications are clearly detrimental to battery life. On average, iOS is more power-conscious and tries to reduce the demand on the processor. The new Android 5.1 Lollipop has gotten much smarter in this segment than its predecessors, but can still benefit from more improvement. Tidbit #2: While the OS should in principle terminate applications not in use, keep an eye on rogue apps that continue to run in the background or when you don't need them. Shut them down or better yet, remove them from your device.

3. Networking and radios: Your smartphone contains several radio systems. A modern device will have a LTE radio and a separate 3G radio, and possibly an older 2G radio. It will have a separate WiFi radio and a bluetooth radio, albeit these two are usually low-power, relatively speaking. These radios have power amplifiers for their transmit-receive functions. These power amplifier consume a lot of power -- to amplify the signal -- when the network signal (the number of bars on the top of your screen) is really low. In other words, if your signal level is low, the smartphone will compensate for that by boosting its own transmission power, hence more power consumption. How much power: what is an average power of 1,000 - 1,500 mW could double or more. Tidbit #3: Turn off unnecessary radios (WiFi, bluetooth or LTE radio if there is no LTE signal). Turn off background data refresh and do not let apps have unfettered access to the network radio (especially 3G and LTE) in the background.

4. Location services: The location services utilize an integrated chip that includes a GPS transceiver complemented by another integrated chip with accelerometers and gyroscopes. A GPS chip will consume approximately 25 mW and the accelerometer/gyroscope will consume another 25 mW -- that's 50 mW in total. It surely is far less than the radio and screen, but in a world of limited power budgets, every mW counts. Tidbit #4: More and more apps are requesting to access locations which turns on these services and consumes power. If you don't need them, turn these background location services off, and limit them to only the apps that are essential, such as navigation. Also, terminate the apps that use location services if you are not using them. Google Maps and other map apps are apps that like to check your location frequently. Terminate it if you are not using it.

5. Data storage: For most users, we don't write into memory very frequently. Memory includes the flash memory in your device (those 32 or 64 GB that hold your files and music and photos), as well as the SD Card that boots your storage by a large amount. But if you are a user who loves to use the camera feature continuously, more importantly the video, then you may be in for a surprise. Each MB file consumes a peak of 400 mW of power to be written into memory. Uncompressed standard HD (1080p) video file is 3 MB per second. Assuming an optimistic 10:1 file reduction after compression, that translates to 120 mW for each second of recording. The newer 4K video format has a whopping uncompressed bitrate of 40 MB/sec. That will be a serious power hog! Tidbit #5: If you want to record video on your smartphone, reduce the resolution to the minimum you are willing to live with. You will be surprised to see how great the 720p quality looks on the screen.

Wednesday, March 11, 2015

56. SOLID-STATE THIN-FILM BATTERIES....WHAT ARE THEY?

Did you know that the European semiconductor giant ST Micro makes rechargeable lithium-ion batteries? Probably not. You don't believe me; go ahead and google "ST Micro thin-film batteries." It's really tiny. It is a square that measures one inch (25.7 mm) on a side, and is a mere 0.2 mm thick (that's about the thickness of a human hair). But before you jump out of your seat to order one, let me tell you that it has a capacity of 0.7 mAh. That's right, that's 0.7 milli Ah. It will take about 2,600 of these little cells to give a capacity equivalent to the iPhone 6 battery. But they are useful for applications that require very little power and energy, such as RFID tags or smart cards.

The cells from ST Micro and other suppliers such as Cymbet and Front Edge Technology represent a new category of rechargeable lithium-ion batteries that are called solid-state thin-film batteries. The name says it all. They are solid-state, in other words, no gels or liquids inside the structure. They are thin-film, in other words, made of very thin layers (films) of materials. Naturally, this implies that they can be manufactured in similar ways to semiconductor chips. This is a powerful argument for manufacturing with high precision yet delivering extremely low cost. So if that is the case, why don't we see them more commonly in mobile devices. Before we tackle this question, let's dive a little into the internal structure of solid-state batteries.

Basic structure of a lithium-ion battery includes two electrodes and an electrolyte in the middle. Courtesy: Wikipedia.

A lithium-ion battery consists fundamentally of two electrodes, an anode and a cathode, sandwiching an electrolyte medium that allows the lithium ions to shuttle back and forth between the electrodes; in battery parlance, it has to be electrically conductive to the ions. The anode and the cathode are commonly made of carbon and lithium-cobalt-oxide (LCO), both of which are solid materials that can be layered down using semiconductor-like techniques. But the electrolyte is usually a liquid or a gel...hence, it defies our stated objective of thin layer deposition. The hunt has been for decades now to find a electrolyte that is suitable for the transport of ions through it, yet be made of a solid material. Unfortunately, very few candidates present themselves so far as commercially viable -- but that has not deterred small and large companies from continuing the search and exploration. Examples include startups such as SEEO in California and Sakti3 in Michigan.

Lithium Phosphorous OxyNitride, or in short LiPON, is a glass initially developed at Oak Ridge National Laboratory in Tennessee and has evolved into the material of choice today for commercially available thin-film solid-state batteries. But it is far from ideal. It exhibits a 1,000X higher resistance to ion flow than do liquid or gel electrolytes. Not good! That means few ions can shuttle back and forth consequently limiting the capacity of the battery to a very small figure, usually on the order of mAh or less. Other exotic candidates include zirconia-based ceramics but I am not aware of any commercial deployment. The result is that the energy density of these cells is low: for the ST Micro cell, it is a meager 20 Wh/l, or 30X worse than state-of-the-art lithium-ion polymer batteries.

The other challenge is cost, presumably driven by the lack of manufacturing scale, potentially low manufacturing yields, and the high cost of the exotic materials. Presently, a small solid-state cell can retail for $10 - $30 each. That works out to more than $5,000 per Wh vs. $0.20 per Wh for commercial polymer batteries. But some of the new startups are trying to change this and reduce the cost by several orders of magnitude.

But on the upside, solid-state cells typically exhibit long cycle life and an excellent safety performance -- they are not prone to fire the same way liquid or gel electrolytes are.

In summary, solid-state thin-film batteries present a very attractive story but much research and exploration in materials need to be completed first. I will continue to applaud for more breakthroughs in this area but I don't see one yet on the horizon.

Wednesday, March 4, 2015

55. AT MWC 2015, BATTERIES & DESIGN ARE KINGS

This year's Mobile World Congress show in Barcelona was buzzing with a number of announcements, with the much anticipated Samsung S6 and wearables taking front seat. All the major players in the mobile space, with the exception of Apple, proudly exhibited their new devices, technologies and capabilities in very glitzy and increasingly spacious booths. In this incredible information frenzy, we can make a few observations about where mobility is heading for the next year or two.

1. Thin is in, and that means headaches with thin batteries:

So goes Apple, goes the mobile industry. That is now very clear. Arguments abound on the merits and disadvantages of ultra thin mobile smartphones, but these are in some sense moot discussions. Apple sets the trend for design and looks, and the rest of the industry follows. Samsung, for a few short-lived years, was a counter pole to Apple, but with the Samsung Galaxy S6, it finally succumbed to the immense momentum of the iPhone. The iPhone 6 is 6.9mm. The Galaxy S6 is a smidgen thinner at 6.8mm. The iPhone has had a non-removable battery since the original one. The new S6 finally adopts a non-removable battery. Side by side, these devices are beginning to look awfully similar, both using an elegant unibody aluminum design. With increasingly converging designs and performance specs, brand recognition and looks now become more important elements in the end user's purchase decision.

With such thin profiles, the battery is getting thinner. Real thin, less than 4mm. This poses serious headaches as both energy density and cycle life performance are degraded.

The iPhone 6 and Galaxy S6 side by side. They look awfully similar.

2. Bigger is better; that is a bigger battery capacity:

With a few exceptions, high-end smartphones are nearly all converging towards a 3,000 mAh battery. These devices exhibit large and full-HD displays that are typically power hungry. With such capacities, the expected battery life is one day, and occasionally depending on usage patterns, up to two days. For mid-range and lower-end phones using smaller and displays of lesser resolution, the battery capacity is converging towards the range of 2,000 - 2,500 mAh.

3. Fast charging is in:

Samsung is the first large mobile device maker to seriously tread on fast charging. Its Note 4 was the first device to offer some fast charging capabilities, at or approaching 0.9C rates. The Galaxy S6 and its sister Edge are also incorporating modest fast charging capabilities, albeit these two devices sacrifice battery capacity (down to 2550 mAh) relative to competing devices from Sony, LG and the new manufacturers from China. More and more devices will launch this year and next with fast charging capabilities. Fast charging is finally becoming a standard.

4. With wearables, the battery remains an utter failure:

Nearly every mobile device maker has already announced or introduced a watch of some kind. Their utility and features are evolving fast. End users have not exactly rushed to buy these new (and expensive) gadgets, but they are certainly keenly watching from the sidelines. The watches announced at this year's MWC are increasingly elegant signaling that functionality is no longer the sole determining driver in mobility -- design and looks are on the minds of the engineers and end customers. But in this evolving ecosystem, the battery fails miserably. The Sony SmartWatch 3 exhibits a battery with 420 mAh lasting about 1.5 days of "average use." The LG Watch Urbane has a greater 700-mAh battery capacity but does not last more than 1.5 days -- it has a power-hungry LTE radio. For both, the charge time is 2 to 3 hours. That's not acceptable. That's far too long for a wearable device. Expect that fast charging becomes an absolute necessity in this product category.

Two elegant smart watches. The SmartWatch 3 from Sony (left) and the LG Urbane (right).