External Battery Pack Confusion

John,

I just read the first couple of questions you asked. I have done detailed testing on one of the two battery packs you are considering (Anker Astro 6700mAH – aka AA6700).

How fast will the battery pack charge?

The AA 6700 has a specified maximum charge rate of 1,200 mAh per hour. I measured the actual maximum charging rate at 1,260 mAh. There are 2 things that are required to achieve this rate. The first is a USB charger with a minimum wattage rating of 1.260 * 5 = 6.3 watts. Apple’s USB chargers are available in 5.0, 10.5, and 12.0 watt options. You would require their 10.5 watt option, at minimum, to charge your battery at its fastest rate.

The AA 6700 specification capacity is 6,700 mAh. I measured its actual capacity at 5,310 mAh. The time to charge from empty is 5,310 / 1,260 = ~4.2hours.

The 4.2 hour charge rate is also predicated on the assumption that you use it with a charge cable that will not drop the voltage below 4.75 volts at the battery input. Whether a cable will do this is primarily based on its length (shorter is better) and the power wire’s gauge (28 is the worst and 22 is the best). I have tested most of the cables on the market. The longer the cable required, the fewer the options that will work efficiently at 1,260mA. For 12″ or shorter cables, either an Anker Powerline or Anker Premium will insure the maximum charge rate.

Can all battery packs take advantage of a “faster charging” wall charger?

No, each battery pack will have a specified and an actual maximum charge rate. In the case of the AA 6700, those values are quite close but, not for all batteries.

There are batteries near the capacity range you specified, that will charge at a specified rate of 1,500mA and a measured rate of 1,666mA to 1,700mA for a faster charge time as calculated above.

FluxMob Bolt 2

I read the specifications for the FluxMob and they do not specify the battery charge rate. They do specify the USB ports can provide 2.4 amps max. All that specification means is that the USB charger component of this package a 2.4 * 5 = 12 watts. This does not mean that the battery will charge at a 2.4 amps (2,400 mA) rate. Without a set of test equipment and a background in electronics, you also wouldn’t know the real capacity of the battery or the real maximum discharge rate.

Their 6,000mAh battery will NOT charge at 2,400 mA without a high risk of exploding. The safe maximum charge rate or “C” rate for a typical USB battery is about .3. So the best possible safe design would provide 6,000 * .3 = 1,800 mA charge rate. The typical charge rate for batteries of this capacity is what I mentioned above (1,200 – 1,700 mA maximum).

I’m not an expert, but what if charge two smaller batteries in parallel? Will it take half the time?

2 x Anker PowerCore mini (3200 mAh, 2.3 oz)

1 x 10.5W charger and Y-type cable

EDIT: I was wrong. PowerCore mini’s input is just 5 V / 0.8 A, so same 4+ hours.

Before reinventing this wheel, Read this Thread.

Richard – thanks for the specific information about the battery pack I mentioned. For the Anker, where did you find the specified maximum charge rate?

To determine whether this rate would be possible, how did you get “5” as a multiple to determine the wattage required to achieve the maximum charge rate?

On Amazon, it says the Anker will fully recharge in just over 4 hours using a 1.2 amp adapter (not included). You reference needing a 6.3 watt adapter. Are the adapters (I assume this means the usb-plug) usually rated in amps or watts?

So if I want to find that information for other packs, I want to know the maximum charge rate/hour? In all of my research, I didn’t find a single battery listing that information in any easy to find place!

Any idea how the Unu UltraPack Go, which has 3,000 mAH, can fully charge in 15 minutes? Sounds like the battery should explode; I guess it’s not a “typical USB battery”? I assumed it was able to charge fast because of the included wall plug, not because of the internal battery itself.

In doing your detailed analysis of the Anker, would you recommend it? Did you test others of similar capacity that you would also consider buying? A few other battery packs I’ve seen have lighting cables built into them, so that seemed convenient (Here’s a Lithium Ion one: http://www.amazon.com/Apple-Certified-1-Pack-Ultra-Portable-built-/dp/B00N54R8K8/). Again, though, I can’t find the “maximum charge rate” (aka “C rate”, right?).

I just noticed too that one of these packs has a Lithium Polymer as opposed to a Lithium Ion battery (http://www.amazon.com/Certified-OLALA-Portable-Lightning-External/dp/B011BEA4V8/). Why might I want Lithium Polymer instead of Lithium Ion? Does this affect the charge rate?

Vyacheslav – That’s an interesting idea that I hadn’t considered. I would like to be able to charge my phone at the same time as my battery, so I’d use the Y cable for that.

Richard – any experience with these “Y” cables? If I have the right watt/amp wall-usb dongle, can I charge my phone and the battery at their maximum charge rates, or does the Y cable reduce the power to each?

I was wrong about PowerCore mini. It’s slow to charge – same 4+ hours.

And for a powerful charger and Y-cable, two smaller chargers with cables might weight the same. 5W Apple charger is 09.oz, 10W Apple charger is 2.35 oz.

John, all USB devices run at 5V, that’s where Richard got the multiplier from. It’s also a handy way to convert between watts and amps. Sometimes one spec is easier to find than he other, but you can convert between them with a simple equation — voltage * current = power. In other words, volts * amps = watts. 1.2A * 5V = 6W, so if Richard’s testing is accurate that ideal charge rate is reached  at 6.3W then Anker slightly underspecced their device.

John,

You asked:

For the Anker, where did you find the specified maximum charge rate?

Amazon’s product description says, “Recharges in a little over 4 hrs. with a 1.2amp adapter (not included)”

To determine whether this rate would be possible, how did you get “5” as a multiple to determine the wattage required to achieve the maximum charge rate?

Mitchell already did a good job of explaining this to you.

Are the adapters (I assume this means the usb-plug) usually rated in amps or watts?

Mitchell already did a good job of explaining this to you.

So if I want to find that information for other packs, I want to know the maximum charge rate/hour?

Yes but, the charge rate is listed as mA (no hour) versus charge capacity with is listed as mAh.

Any idea how the Unu UltraPack Go, which has 3,000 mAh, can fully charge in 15 minutes?…I guess it’s not a “typical USB battery”?

Yes and yes. It uses a special 9 volt / 3.6A charger in combination with a special “Ultra Fast Charging” battery. The battery is optimized for fast charging rather than providing power efficiently. Both Unu battery options will only provide 35 – 57% of what the specified capacity states when output via the USB port. For your iPhone 6S, the Unu Go will only charge your battery ~one time. Most UL backpackers have the most important selection criterion as “actual power output via the USB” versus “actual weight”. The Unu type batteries are by far the worst option available regarding this criterion. Another problem with this type of product is the charger takes 2-3 power strip spaces, which may get you in trouble with your fellow backpackers if power strip space is not available for them.

Source: Battery University

In doing your detailed analysis of the Anker, would you recommend it? Did you test others of similar capacity that you would also consider buying?

Yes, Anker is a quality battery. The AmazonBasics batteries test a little better regarding the primary UL Backpacking criterion mentioned above. In addition, they have a faster charge rate than the Anker’s for thru-hikes.

Why might I want Lithium Polymer instead of Lithium Ion?

You should ignore this distinction. What marketing departments are calling “Lithium-polymer batteries” are actually “Lithium-ion polymer” batteries. “Lithium-polymer” batteries are almost exactly the same as lithium-ion batteries, but they are instead contained in a flexible polymer casing. It’s basically just a repackaged lithium-ion battery.

…any experience with these “Y” cables?…can I charge my phone and the battery at their maximum charge rates?

There may be a problem using a Y cable or splitter with the iPhone if everything is brought up at once. The iPhone uses a protocol to determine its maximum charge rate and then expects that full amount or quits charging. The USB batteries take what current is available. Theoretically if you: plugged the iPhone into the charger and let it start charging and then plugged in the battery, you should be OK but this is not the optimal solution.

Your iPhone 6S can charge at a maximum rate of 1.7A and the AmazonBasics batteries can charge at a maximum rate of 1.7A for 3.4A * 5 volts = 17 watts. The optimal solution is an iClever BoostCube 4.8A 24W Dual USB or similar product.