At the heart of the new, real personal computers are batteries. Ironically, while technology has changed by leaps and bounds the last two decades, battery technology is much the same. The Duracell and Energizer batteries you find in stores today are the same as the ones I bought in stores as a teenager, many, many years ago.

To compensate, developers incorporate all sorts of techniques for using less power, whether it’s turning off wireless radios, slowing down processors, and dimming screens. In my experience, Apple has done a particularly good job in this area, in fact I think the most significant aspect of the iPad is the fact that it easily makes it through the day on a single charge. Every time that I watch baseball for hours on end using my iPad, I am amazed at how long the battery lasts with the screen on and the WiFi radio working for hours.

Still, despite the improvements that have been made, if you carry around your computers throughout the day at some point you will become concerned about whether there is enough charge left in the device. To compensate we often buy extra chargers to have at the office and at home, and include a charger in the car so that we can top off batteries during some of these down times.

The problem becomes more complicated when carrying multiple devices, and a few months back I bought a Powerbag that has become an invaluable part of my computing toolkit. Powerbags have built-in batteries and power cords, and are available as backpacks, messenger bags, and brief cases. I own the Tablet Messenger bag, which has a stylish design and room to carry a 9″ tablet (iPad) or smaller, and two smartphones.

The Powerbag Tablet Messenger comes with a 6000 mAh battery that can charge a standard smartphone four times, and has Apple, micro-USB, and mini-USB cords, plus one standard USB port. The Tablet Messenger is optimized for Apple fans as the Apple cord is located in the only outside pocket on the front of the bag, perfectly sized for an iPhone or Android smartphone. One can also charge an iPad at the same time by plugging in its charging cable in the USB port. An improvement that I would like to see with the bag’s design is interchangeable power tips that would allow me to change the Apple cord to a micro-USB cord, or vice versa.

I was disappointed to find that my Samsung Galaxy Nexus does not charge on the built-in micro-USB cord, apparently the Galaxy Nexus has a non-standard charging requirement. Fortunately, the Samsung Galaxy SII I have for work does charge on the micro-USB cord. To charge my Galaxy Nexus I carry a micro-USB cable that does work and connect it to the USB port, but that also causes me to constantly swap that cord with the USB charging cord of my HTC Flyer because unfortunately the Flyer has a non-standard charging port. (Boo, HTC!) I have never used the mini-USB cord as none of the computers I carry with me now have that port, so if Powerbag isn’t going to provide interchangeable tips on the cord, I recommend they replace the mini-USB cord with a second micro-USB.

The Tablet Messenger bag has a removable shoulder strap, a very well padded handle at the top, and is small enough to fit inside the main compartment of my rolling eBag Backpack that I use every day when I go to work. For each of my commutes I plug in my smartphone and HTC Flyer to top off the battery, and any time that I carry the Tablet Messenger to an appointment the devices inside are charging.

Every couple of days I charge the bag’s battery, which plugs into a dock that is attached to the bag. If you have devices connected inside the bag while charging the battery, the devices charge first before the battery re-charges, which means that while traveling you can simply plug in one cord to charge the multiple devices in the bag. On front side of the bag is a button that you press to check battery strength as well as turn on charging.

The Tablet Messenger Powerbag costs $139 direct, but can be found for a little cheaper on Amazon and other third party sites. As I said, this bag ships with a 6000 mAh battery, but I have recently bought a 9000 mAh battery for $59 to extend the length of time between recharges. I can carry the original 6000 mAh battery with me if I like to have even more recharging power if I am on extended trips.

Like many gadget fans, I am constantly on the lookout for stylish bags to carry my gadgets around. The Powerbag Tablet Messenger not only looks good, but it provides a much needed additional benefit of charging my computers. For me, the Tablet Messenger is perfect for my needs, but if you need to carry larger computers, you can check out Powerbag’s backpacks and messenger bags.