Saturday, March 29, 2014

USB battery bank

My new Nexus 5 eats through its battery a bit faster than I'm used to, and I've been thinking about getting a power bank for a while anyway, so I decided to look around earlier this week.  I went for a cheapo off eBay.  The unit pictured below cost $18 shipped from a US vendor.

It seems to work just fine. I plugged my phone in at 71% charge, the battery bank arrived showing 55% charge.  I used the 2.1A plug, it topped the phone up in less than an hour and the battery bank still shows 54% charge. It claims 12000 mAH.  From the size of the thing, I'd guess that it holds four 18650 cells, so that does put it over 10,000 mAH at least, though not at 5 volts, but you totally expect these things to be rated in the most over-the-top way they can vaguely justify.  In any case it should be able to quickly boost a dead phone up, and it should be able to do it at least 4 or 5 times before being dead itself.  For < $20, I'd call it a winner.

The LCD is backlit, the backlight times out after about 15 seconds and the LCD continues to display. It shows if you have something plugged into the 1A or the 2.1A socket (I assume both can be used at once). It has a little LED flashlight that can be switched on/off by double-clicking the power button from either on or off state, and a long press on the power button turns the unit off.  The unit also powers itself down after the power draw goes away, though I doubt it would shut down when the phone is done charging since I think most phones are going to keep drawing a little power.

It comes with a short USB power only cable with tips for MicroUSB, MiniUSB, Apple and a little coax that I've seen used by Kyocera and a few other things.  The power-only cable is also useful for using with public charging points if you're paranoid about plugging your phone into a random wild USB socket (since it's possible to build such a point that would strip data from your phone or even infect it if you use a full data/sync cable).

FOLLOW UP: It doesn't actually have all that much capacity. I plugged my phone in last night at 30% charge. In the morning my phone was at 100%, the bank said 74%.  This evening I plugged the phone in at 28%, and the bank went dead with the phone still at 80%.  Maybe a few cycles will improve it, but probably not all that much.  It seems to have perhaps 5000 mAH at 5V, which at 100% efficiency would translate to about 7000 at 3.6v (which the cells inside would nominally be at) not the 12000 that they claim.  If it had really good cells inside, like Panasonics or something, it might reach 12000.  Still, it's fine for my purposes and I can't complain for the money. You have to realize going in that these things have ridiculous ratings, like the $20 eBay bike headlights that are rated at "2100 lumens" - they actually put out about 1000 lumens, which seems bad but even 1000 lumens for that money is a good deal.  Just realize when you buy that specs from these places are generally overstated by as much as double.

1 comment:

Unknown said...

I have a couple of those, one from Anker (not the cheapest of suppliers) is rated at 15,000mAh actually achieves quite close to that.

I recently picked up one that is metal-cased, rated at 4400mAh and doubles as a handwarmer (useful in the winter, as I suffer from Raynaud's) Don't know what the efefctive capacity is yet, but it certainly stays hot for quite a few hours on a single charge. It has a pair of 18650s inside (of *course* I pulled the lid off after purchasing...) so 4400 is a bit of a stretch.

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