Laptop External Battery Roundup

Laptop External Battery Roundup
By

Battery life is always such a big deal in our mobile coverage (often because gaming systems fall so short). But don't feel limited by the built-in power source. Today we round up 15 external batteries that can keep you running longer away from a socket.

This article originally appeared here on Tom’s Hardware. It has been edited for the busy IT pro. Please see the original for details excluded here and for information on how to buy products featured herein.

Shopping for a notebook involves a delicate balance between battery life, performance, usability, and price. No two users share the exact same criteria for what they consider the right blend. That’s why we try to evaluate mobile platforms based on their perceived strengths. Take last year's Netbook Buyer’s Guide as an example. We considered the fact that some buyers are willing to spend more for battery life and forgo a bit of performance. Others are willing to pay an extra $100 or $150 to get both. Another group cares more about usability. The list of ways to break even this one specific market into tiny pieces goes on and on.

If battery life is your number one priority, shopping choices are limited. Clearly, there are notebooks designed for those on the move. But what if you don't want to sacrifice elsewhere to get that mobility? Maybe you just need another hour of run time to get your current notebook through the day. If that's the case, a brand new system doesn't make much sense. 

Even if you already own a notebook that delivers ample battery life, we're certain that there are travel days when even a power-sipping system just doesn't have enough juice to last through closing time. If you spend a lot of time on the road, layovers don’t provide enough time at an AC jack to get you back to 100%. That might mean your in-flight entertainment gets interrupted right before the big climax. Sleeping, talking to unwilling neighbors, and hitting on flight attendants only eats so much time. What other options are there?

External BatteriesExternal Batteries

There is a solution, though. Check out an extended laptop battery, which comes in the form of an even larger installed battery pack compatible with your existing system. There is a big catch. These batteries (often denser six-cell or nine-cell) weigh down your machine, altering its mobile profile. These batteries stick out the backside of your notebook like a sore thumb, and can turn a sleek thin and light notebook into a clunky desktop replacement.

Fortunately, there is another option, too: universal extended batteries. These batteries don’t plug into your system directly. Instead, they function similar to uninterruptible power supplies (UPS), which we often associate with safeguarding desktops. They are always external units, but often have a small profile that makes them easier to pack for travel, offering higher densities than extended batteries can't provide. And if that wasn't enough, you generally get the ability to charge your cell phone, iPod, and camera from them as well.

After we published our Netbook Buyer’s Guide, one reader posed a question about mobility in the comments. So, during the past two months, we hunted down just about every available solution capable of extending the battery life of your notebook. If you're on the go, this story is for you.

We are listing the total capacity of the batteries here, but we want to point out this isn't always an apples-to-apples comparison. mAh is the SI abbreviation for milliampere-hour. This is a quick and dirty way to compare the relative energy stored in one battery to that of another. However, these comparisons are only useful if you are looking at same battery chemistry.

If you want to think of capacity as how much fuel the battery holds, like a tank of gas, then chemistry is the type of fuel. If you are comparing lithium-ion polymer to nickel-metal hydride batteries, you might as well be talking about diesel and gas-powered cars. Also, think of the huge energy difference between one pound of coal and one pound of uranium.

Inside Your Laptop: Power Distribution

Remember your desktop system? The power supply has 5 V, 3.3 V, and 12 V power rails. Those exist on your mobile system as well. But on a notebook, the power brick doesn't deliver those three voltages to the motherboard, as a PSU does. Instead, the brick delivers a steady voltage to your notebook's input connector. After that, voltage regulators on the laptop motherboard do the rest of the work to output voltages that the CPU, graphics processor, storage and add-in cards can use.

Displays are a different beast altogether. Older CCFL LCD panels need a voltage higher than what your notebook’s power supply can deliver. In order to achieve that higher voltage, a component called a power inverter is used to convert back to a low-frequency AC current. The existing generation of notebooks use LED-based LCD panels, which don't have this high voltage requirement, as they are solid-state devices. Instead, LED backlights operate off of +5 or +12 VDC. LEDs use less power than CCFL backlights; additionally, the lack of a power inverter translates into better efficiency as well.

How does the battery all tie in? The battery supplies power to the input side of the regulators, just like power coming from the wall socket would if you connected that way. However, there is a separate charging circuit. This diverts power from the AC adapter before it gets to the voltage regulators so that your battery charges. This charging circuit is the reason why the voltage on the AC adapter is always rated higher than the one stamped on the battery. You need a higher voltage to charge your battery.

Extended batteries are unlike the battery that ships with your notebook. The most obvious difference is that they come with a variety of tips, since they claim universality with each manufacturer's specific power connector.

Even within a single brand, it is possible to find notebooks that use different voltages or plug sizes. For example, Dell has a standard plug size, but the Inspiron Minis are exceptions to this rule.

The stock power adapter that ships with your notebook supplies voltage at a fixed setting. This is not so for the external batteries. In order to deliver the multiple voltages required by different devices, they must also be capable of outputting different voltages.

There are a couple of ways to do this. The easiest way is to use a voltage converter controlled with a manual switch. Some companies choose to go a step further by using a sense resistor in the adapter tip. The sense resistor drops the voltage as current crosses its path. The small voltage drops are fed to a simple comparator circuit, which is then used to control the VDC output from the power supply.

If the resistor is in the tip, there is an additional layer of protection because you cannot force an incorrect voltage over a plug. Physical switches give you more control, but there is a chance that you'll choose an incorrect voltage and damage your notebook.

The way voltage gets to your notebook is important to understanding how an external battery can affect run time. Say your internal laptop battery yields two hours and your external battery offers an additional two hours. If your notebook is at 50% and your external battery is at 100%, this doesn't mean you get three hours total. There is an efficiency loss involved whenever you make an energy transfer, and you see this happen whenever the external battery charges the internal battery. This ineffiiency is less than what you see with an AC to DC conversion if you were to use a UPS, but it is there all the same. Remember that this only applies during a transfer of energy from battery to battery. If your notebook was at 100% and external battery was at 50%, you would see three hours total.

Andrew Ku is an editor for Tom's Hardware. He works closely in the main lab with the Editor-in-Chief, Chris Angelini, developing benchmarks and covers a range of topics from storage performance to mobile devices.

Comments