4xAA USB battery case – version 2

I’ve been making some research over the past few years looking for good solutions to power up my devices. Selecting a mobile power source is really a question of how much current and voltage your electric device consumes, and how much weight you’re willing to carry.

When I travel, I usually carry with me a PDA, a camera operated by 4xAA batteries, a hard-drive based OTG backup device and a 4xAA charger. During my previous journey, I hacked a 4xAA battery case that I recieved along with my ELOOK LK-A6 OTG device, so it could also charge my PDA (back then it was AXIM X5). It required soldering a 3.5mm DC plug directly into the battery contacts. It worked great, but things changed, and I needed some adjustments.

For my next journey, this setup has not changed much. I’m still carrying a 4xAA based camera, the ELOOK LK-A6 (unfortunately nothing better has come out yet), and a new PDA, the HTC TYTN II.

This time I decided to make the battery case more USB-oriented. I drilled a hole in the case, soldered a USB port that I excavated out of an old USB hub. I also soldered a USB extension cord directly to the battery contacts.

The great thing about using AA batteries is that four of them can supply enough current to power up a 2.5″ hard-drive, or for my case – the ELOOK LK-A6.

Four rechargeable batteries give you 1.2V * 4 = 4.8V which is almost 5V – the required voltage for USB! Now since my batteries turn out to be slightly over-charged to 1.3V, that gives me the required 5V. Sufficient for every USB-based device.

The battery case that arrived with the ELOOK LK-A6 didn’t include any electric circuit or any kind of voltage stabilization. This is a direct connect to the batteries (connected in series). It worked without a problem powering many of my USB devices.

Modding the AA battery case

After soldering two USB ports into the AA battery case I can practically power any device that works on USB. Notice that the USB extension cable can’t supply enough current for a hard-drive. I used a low-quality thin cable that is suitable for USB 1.0 devices. If you’re planning to build one for yourself, get a proper USB 2.0 cable, or simply solder the USB female port directly.

You should be aware to the limitation of 4  AA batteries. Although they can power-up a 2.5″ hard-drive, as the batteries drain, the current drops down, which means they will not be able to supply enough current for high consumers, such as hard-drives, after some time. However, you will still be able to use them to charge other things, such as a PDA or using a camera.

How to solder – testing that it works

Cut the extension cable to the length suitable for you, then strip the USB extension cable, you’ll see two wires (might be red and white). Get yourself a cheap USB lamp to make the tests. Connect the lamp to the USB extension cable. Make sure there are four batteries inside the case, put the red wire on the Plus side, the white wire on the Minus side. Do you see any light coming from the lamp? If you don’t, switch the wires. When you find the correct polarity, solder the wires and close the case.

Soldering an actual USB port is a little more tricky. There are four tiny metal threads inside the port. The plus and minus are the left and right ones. It doesn’t matter which is which. Solder two wires to each thread. Be careful not to make contact with the two threads in the middle. You can take them out so they will not interfere using small pliers. Connect your USB lamp to the USB port, repeat the same test as before with the wires you soldered. When everything is working, solder the other side of the wires to the batteries’ contacts.  You’re almost done! Now you have to carefully mount the USB port to the battery case so it will not move. This is realy important since you are likely to push and pull this plug many times while using it. Close the case and you’re done.

Surely, there are better ways to do it. This is the simplest way that I can explain.

Carry a few sets of batteries with you

Since I have  a camera based on 4  AA batteries, I carry with me three sets of AA batteries. First one is in the camera, second one is in the battery case, third one is for backup.

So you need to power up a hard drive and your batteries are drained out? No problem, use the other set!

How to overcome AA batteries disadvantages

In my previous journey I learned that the last sentence doesn’t always apply in reality. Maintaining three sets of AA batteries isn’t easy. You have to remember which one is drained so you can charge it as soon as you get back to your hotel or hostel. Moreover, cold weather can easily effect NiMH AA batteries. You might find yourself with drained batteries although you charged them a few hours ago.

After I returned from my last journey, I searched for solutions that can prevent that from happening in the future. I found two type of things that can help: Li-ion USB batteries and LSD AA batteries.

LSD AA Batteries

A little miracle called NiMH LSD – Low Self Discharge. These batteries have smaller capacity compared to the regular NiMH batteries (2000mAH vs 2700mAH), but they can keep their charge for a long time (many months). More importantly they can work in cold temperatures. There’s nothing worse than climbing on a mountain, feel the temperature drop, and discover that all your batteries are dead.

Li-ion USB batteries

The other solution is using a rechargeable Li-ion battery stored in a special case that has a USB output. These are the same batteries found in mini-cameras, laptops, PDAs and other devices. They are usually refered as propriety batteries becaus they can be shaped to fit a device, unlike AA batteries which have a standard shape.

There are two problems using a USB Li-ion battery case.

The first problem is the voltage: Li-ion batteries have 3.7V to 4.2V voltage (when fully charged). It’s not enough to power USB devices. Many of these Li-ion battry cases can’t even supply enough current to power up a hard-drive. The case should have a well-planned voltage booster from 3.7V to 5V. This doesn’t go without a cost. You may lose upto 30% of the original capacity while boosting the voltage to 5V. For example, I have such a device that holds 2000mAH. The electric output, as stated on the case is only 1445mAH.

The other problem is the one-time-use till next charge. Unlike the AA battery case, you can’t replace a Li-ion battery in this kind of case. These batteries are not common like the AA batteries so even if you wanted to, you can’t buy them in a store.

The Li-ion batteries are unable to supply high current for a long period of time. As they lose their charge, the current goes down to a point where they can’t power up a hard-drive even after a couple of minutes.

Their real advantage is their relatively small size compared to AA batteries.

Using a AA battery case together with Li-ion case

Due to the rather small size of the Li-ion battery USB case, I find it very convenient to carry it along with the 4xAA battery case. The amazing thing is that even when one of the cases can’t supply enough current, together they can. Using a split USB cable, you can connect a 2.5″ hard-drive to both cases, while the batteries are substantially drained, to give it enough current. A split cable adds up the current, not the voltage. Thus,  connected together I can continue using the power when one of the battery cases is drained, even though it wasn’t usable if I only had one of them.

I will write a few more words about Li-ion USB cases in a future article.

Note: I take no responsibilty for anything that might happen to your devices or to you by following the steps described in this article. You should deal with soldering and electricity only when you know what you’re doing.

Canon S3 IS

First, I will describe my needs. I planned a two months journey to the far east, into countries where electricity is not always availiable, equipped with a Canon S3 IS camera and ready to take as many pictures and video clips as possible. Thailand is a well developed country that offers many places with access to the internet and other places that allow you to burn your images on a CD for a small fee. That is not the case in Cambodia and Laos, the two other countries I’m about to visit during my journey. There are places in Laos that have electricity for a few hours a day, and in others none at all. In some areas, Cambodia is not too far behind. Travelling in these countries requires a lot of patience. Even a person who is used to wait 30 minutes at the doctor’s office while doing absolutely nothing, would find it very difficult to do the same during the tough rides (4 to 12 hours bus-ride) between some of the remote cities. You must have some way to make your time more pleasant. It can be by chatting with the locals, reading a book or anything else that can pass your time.

What to take?
One can take a lot of devices, starting from a laptop, PSP, other gaming platform, MP3 Player, MP4 Player, PDA, and more. The real question is what do you want to do.I chose to not carry a laptop. It is too expensive, too heavy and too big to carry around. It does have a high-capacity hard-drive but it’s useless if you can only use it for three hours a day, considering that electricity is not always there.

Storage
Storage is a very important factor for me. A fast calculation for image and video-clips per day showed me I need at the minimum 40 GB of data for a 60-day journey. This could easily climb to 60 GB. I had a couple of options for storage: Hard-Drive, Memory Cards or burning CDs (2-4$ per CD). Even though the prices of memory cards are dropping all the time, 40 GB of memory cards is still very expensive. Add to that fact these cards will not be used after this journey, and you get a lot of money wasted. Burning CDs is popular among photographers, but for a period of two months it can also become very expensive and heavy. 40 GB can be stored in 58 CDs, not including backups which totals 116 CDs. Multiply that with 2-4$ and you get 232-464$ for 40 GB including backups. My last option was using a device that has a built-in hard-drive. There are a couple of solutions for that. One of them is a PSD (Photo Storage Device). This device is based on a hard-disk and its main purpose is to backup photographs from either a memory card or an external device using a technology called OTG (On-The-Go). Another solution is using a hard-disk based media player like iPod, Archos and others. Some of these also use the OTG technology to transfer files from external device; others have a USB Host. To make a story short, OTG has two versions: USB 1.1 and USB 2.0. All of the media players I’ve seen that has OTG or USB Host, can support only USB 1.1 which means very slow file transfer. When you want to transfer 1 GB per day to one of these devices, you end up wasting the internal battery as well as your time. This solution might be suitable for some, but not for my needs. I should mention that there’s another way to backup files into a hard-disk by using a standard external 2.5″ case along with a PDA that has support for USB Host, and by using the PDA’s SD slot you can read the photos from the card and copy to the hard-disk. However, I’ve yet to find a PDA that support USB Host 2.0, so the connection is still very slow for large file transfer.

ELOOK LK-A6

Which PSD to Get?
After deciding on the type of storage device I was going to use, I had to choose the right PSD for me. There are a lot of PSD’s in the market. Many of them are hard to get. The most popular one is the Digimate. Digimate has some versions and most of them operate on the same principal: a card-reader and a hard-disk in the same device. Put any type of memory card (SD, CF, XD, etc..) in the the device, click a button and the content will be copied to a new folder in the hard-disk. Sounds pretty cool, no? The truth is that Digimate is sufficient for some. However, there was no way of making sure that the data existed on the hard-disk without connecting the device to a PC. Moreover, you could not manage the files that you have transferred which means that if you have backuped the same card twice, you’re stuck with multiple data. If that’s not enough then you must know that you’re limited to the card formats that the device would offer. With the SDHC format on its way, all the Digimate-type devices looked pretty useless for future use. Another type of PSD is one that uses OTG and USB Host 2.0 which enabled fast file transfer. These devices are smaller because they do not have any built-in card reader and only have a USB socket into which devices should plug-in. Compatability is the main concern in these devices, because if the PSD wouldn’t recognize your external device, you’ve got a problem. However, this can be solved using an external card-reader mostly. The real reason that made me look into this type of devices was the ELOOK LK-A6. This one had a new ability I’ve never seen before in a PSD: 2-Way OTG. This means not only can the PSD copy files from an external device to the hard-disk, but it can also copy files from the hard-disk to an external device. Sounds interesting? The ELOOK LK-A6 was an unknown device outside of china and I had a lot of difficulties finding information about it. Not only could you copy files, but you could also browse the files on the hard-disk, as well as delete either files or folders. By no means it was perfect. The best example I can give is the poor support for showing filenames. It cannot show long filenames which can be a little frustrating, but when considering its outstanding abilities as a stand-alone device with a very advanced technology and also its relatively cheap price, you can not say no to that. The LK-A6 started selling at the end of 2005. I’ve found another no-name device labeled DigiBay around October 2006, but information about DigiBay was more obscure and considering it didn’t offer anything better than LK-A6, I didn’t consider it at all. I still can’t give a thorough review on the ELOOK LK-A6 because I’ve only had it for a couple of weeks. I will give updates regarding this device in a future article. I will say this: new options have opened to me since I chose this 2-Way OTG device especially in terms of a mobile inexpensive huge video library.

Dell Axim X5

Battery-Life
They don’t make them anymore like they used to. My 3-years old Dell Axim X5 has many flaws, but in one aspect it is unbeatable (as far as I know): Battery-Life. I’ve used a lot of PDAs but none of them had the battery-life of the Axim X5. A couple of months ago while planning my journey, I was thinking whether it’s wise to bring a PDA to such a place where a PDA can be easily broken or stolen. The value of the Axim X5 today is not so high after over 3 years in the market. It is capable for movies, music, games, and has a relatively strong CPU considering its age. My decision to bring my Axim X5 to the journey was made after I found an incredibly cheap high capacity battery for it on eBay. A capacity of 3400 mAh is something that PDAs today can only dream of. After the era of X5, manufacturers, including Dell, started to make PDAs smaller and smaller, shrinking everything including the batteries. With all the new features added to the latest PDAs today like Bluetooth, Wi-Fi, strong processors, and more, battery-life of these devices can be extremely low. Buying another propriety battery is not an option, it’s a must if you want to be out for a long period of time. The 3400 mAh is one of its kind in either price and capacity. It’s a little bulky but when you want to be free of electricity for a couple of days while using your PDA for watching movies and other battery-draining application, this high capacity battery is a blessing.

Propriety batteries
I don’t like propriety batteries. Don’t like them in cameras, MP3 players, and any other device other than a PDA. I would prefer that most of PDAs had a similar battery, but unfortunately it’s not always possible. When I was looking for a new camera, I had in mind two things: AA batteries and SD card. SD card because I already had a bunch of SD cards, and AA batteries because they are cheap and you aren’t obligated to buy a highly expensive backup battery that will be good only for a specific device and die after two years (both of the batteries).

Overall, the ability to be mobile without electricity was very important for me. I had a couple of power-consuming devices which could survive a rather long period of time without electricty. My Canon S3 IS was operated by four AA batteries. These batteries can be purchased for a small price almost everywhere. I had an advanced PSD with a 80 GB hard-disk that was also powered by four AA batteries. Lastly, I had my Axim X5 which had a high capacity 3400 mAh propriety battery, not typical to a normal PDA. Together with three sets of Ni-MH rechargable batteries that could backup both devices in a case of need, I was well prepared for no-electricity sitsuations. If that is not enough, I’ve hacked the battery case that came with the LK-A6 and converted it to a mobile charger for my Axim X5, a charger that enabled me to leave the original PDA’s charger at home.

Now I have a PSD which is also an external hard-disk. I can use the PSD to store movies that were encoded especially for a PDA and transfer them from the PSD to a SD card reader, take the SD card and watch the movie on my PDA. This is mobility in action without using any desktop computer.

Summary
This set-up I’ve come up with is perfect for my needs, but not for everyone. To be completely mobile for a long period of time, mobile from computers but also from electricity, is an amazing ability, but as you can see, it doesn’t come without paying a small price. Together with a small fast AA charger, this whole set-up weighs about 1.7kg inside a small Samsonite Trekking bag. Pictures will come soon.