External Battery Roundup: Stay Away From The Wall Socket

Background: The Technical Stuff

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.

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  • sylvain
    Interesting read. Would it be possible to do a similar test for pure USB external batteries. Used for adding that extra bit of juice to an iPad, iPhone or similar devices?
  • Anonymous

    I am interested in using the battery for a DSLR video rig, i want to use the 12v to power the camera, then split the 5v to power both an asus wicast and a SDI to HDMI down convertor. both these last two devices take a 5v feed. would this be possible do you think?
  • Spanamana
    I purchased one of these batteries from a UK supplier and have to say I have never encountered such poor customer service in a long time. They claim that they supply one free tip a year. Rubbish! When you try to get one for a iPad 3 or later, they charge you $10 because they changed the name of it from "tip".

    After 8 months the battery started not keeping its charge. I tried to use the 2 year warranty to get it replaced and found out that although the unit is guaranteed for two years, the battery is only guaranteed for 6 months. Then I was told that it would cost too much to get it repaired as there is no UK repair centre and therefore there is a charge of $30 for a replacement.

    Having delivered the replacement battery, I have not received a VAT order for £21 for import duty from TNT. So a battery that cost me £50 has now cost me £95.

    Shonky product, useless service. Don't waste your money.