Iphone users know how often "emergencies" crop up when they forget to recharge their phone up the night before. You know your battery isn't going to survive till the end of a long day when you leave your house in the morning with 60% charge or less, especially so when the phone serves up many different purposes in 1 single day. I find that the need for a portable charger arises most often when I am heading out with my friends for a day packed with activities. A day like this will mean that I won't be coming across any free power sockets, and even if I do, I probably won't be in one place long enough to get a substantial charge. So, this is where my "emergency" charger comes in.
In simple terms, an "emergency" charger is a battery encased with a circuit board and a connector that charges the internal battery of a phone, nothing more. At this point in time, I have two of these little critters. One handed down from my dad. Typically, these chargers contain a Lithium-polymer battery, the same type of battery that is inside an iphone. This type of battery have the highest charge density and adequate performance to provide substantial energy to your phone. To me, it is the best battery type for the job because other battery types such as Alkaline, Carbon Zinc or even Ni-MH rechargables just do not have the juice to give an iphone a good charge. Sure, carrying more of these batteries will mean more charge but it is worth the trouble?
So, here's mine. It looks suspiciously like SKU18197 from dealextreme except that the battery capacity is a little different.
Polished metal top surface. The button on the right is for checking the amount of charge left.
It says 1900mAh at the back but it is not going to be easy to verify.
The front portion has a protruding connector for charging the iphone.
While the back port is for recharging the unit. Entirely compatible with the original USB charging cable.
The blue indicator leds light up when charging. It fits quite well despite having a protective silicon cover in the way. Also, the connector fits well despite being a non-official iphone product - it is not too loose and it feels quite sturdy. I feel confident enough to put it in my bag and let it do its business. It does get slightly warm when charging and does not produce a high pitch inductor whine (common for cheaply designed circuits).
So how fast does it charge?
To test this charger, I set the alarm for every 15 mins (except the last reading which is 10mins away) to check its progress while it is charging. The wifi is turned off while 3G and cellular data is left on to reflect typical "standby" drain from the iphone. My phone's initial charge is 38% and I ended my test with 83% - an increase of 45% charge. As this is to test the charging speed, I did not completely drain the emergency charger. Typically, it gives me about 50% plus and minus 5% depending on my phone usage. The charging speed is fairly constant, providing an addition of 10% charge for every 15mins. This is consistent with the fact that the iphone can be set to charge up at constant rate (possibly USB charging current of 500mA), which is about half the charging speed from using the original wall charger.
Overall, I think the charging speed is sufficient. Moreover, the faster the emergency charger charges the iphone, the more strain it puts on the battery, resulting in more heat, less usable capacity and lower number of charge cycles. These are physical limitations that must be considered during the design to give the maximum battery boost to the iphone given the limited capacity and the small size of the emergency charger.
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