Yoga 2 Pro, Etekcity 16Ah power bank and some additional measurements

Question

Hello guys, this would be my short review of Etekcity Wingman external battery I use with y2p. As you know, the y2p battery performance is a little disappointing for a Haswell ultrabook (at least for some), so it's a good idea to have some additional external battery beforehand. After some research I found the interesting candidate, the 16.000 mAh external battery manufactured somewhere in chinese factory (Shenzen?) and then being sold under many different brands (I found at least 5 of them on Amazon). I bought the Etekcity Wingman, as it was the cheapest, for 69$
No links here, but you will find it easily. It has a classy aluminium shell, very good overall build quality, features 5V USB output and additional 12, 16 and 19V outputs with many different plugs. There is no rectangular Lenovo Yoga tip, but in the package you can find the Lenovo X1 big circular plug. So you need an additional converter Cable Adapter from Lenovo, part no. 0B47046 and voila, everything fits.
This external battery can provide up to 19V and as you are aware, y2p needs 20V. But this is not a problem, it's only 5% difference and nothing to be worry about. As to the amperage, the battery can provide max 3A at 19V and y2p original power adapter is rated at 3.25A - but this is not a problem either, as during my actual measurements I never saw the current more than 3A (more about it later).
16.000 mAh for li-po cells 3,7V gives about 59Wh of power capacity and this is important. The internal y2p battery is rated 54Wh, so 'theoretically' the external battery should more than double our y2p working time. Well, theoretically, because: 1. as for chinese products they almost always overrate battery specs 2. there is a limited efficiency for internal voltage conversion inside the battery electronics, so there are some losses (heat).
So, what is the REAL capacity of this thing?
I did a test. I depleted internal y2p battery to 20% and then I plugged in the Etekcity Wingman, set at 19V. It was able to charge the WORKING laptop for 1 hour and 25 minutes and y2p battery charged from 20% to 85% before the Wingman shut down. It was a little warm while working, but not hot at all (aluminium shell dissipates heat very good).
What it means is that this external battery was able to provide about 2/3 (65%) of total internal y2p battery capacity and during that time the laptop was working consuming additional energy from the Wingman (70% brightness, wifi/BT on, some light browsing, nothing demanding). I am estimating that if the y2p was depleted completely and shut down, then the external battery would be able to charge it to about 80-85%. I find this result pretty good.
So if you are able to achieve some 6.5h on internal y2p battery, this external battery gives you another 5h more, for total 11.5h working time out of the socket. Not bad.
I have a laboratory digital power source, so I was able to do some additional interesting measurements (thanks to the cables and adapters):
1. The Yoga 2 Pro starts charging at about 16.5V voltage level(!) Anything lower - it won't charge, higher - it will (no BIOS warnings whatsoever).
2. The charging current for non-working laptop is about 1.6A (I did not set quick charge at Energy Manager).
3. 70% brightness, "daily" power mode, wifi/BT on, keyboard lighting on and doing some lazy internet browsing needs about 470mA of current (averaged, idle is about 415 mA, as each wifi activity creates current jumps). For 20V it gives 9.4 Wh of power consumption and for 54Wh y2p internal battery it gives about 5h 45min of working time. Lets set this situation as a "base" level.
4. Same as above, but power mode changed to "stable". Yellow turns mustard, but brightness intensity remains at 70%. The current goes down to about 420mA (50mA less!). It gives you additional 40 minutes for a total 6h 25min of working time.
5. Same as above, but keyboard light is off. About 20mA of savings, + 15 min for a total 6h 40 min
6. Same as above, airplane mode (wifi/BT off) - another 20mA of savings (not much), but there are no wifi current spikes so it's like idle mode - about 330mA of current consumption, giving about 8h 15min of working (word editing etc.)
7. Same as above, 50% brightness (still pretty usable) - 305mA for a total 8h 50min of working time.
8. Same as above, but with 16.000 mAh external battery - well, you figure it out (+80%)
Happy New Year!

Answer 1

20V/3.25A means that if looking for an external power bank for your y2p the voltage must be exactly 20V and the amperage must be 3.25A or more (3.25 is minimum value). These are perfect values.
But in real world some little deviances are permissible, like 5%. 19V and 3A are examples and I made sure that my external battery rated 19V/3A works good with Yoga 2 Pro. There are more 19V external power banks than 20V models out there and I've chosen my Wingman battery because it was really cheap. But it is always better to find one that meets voltage/amperage ratings perfectly.
The Energizer XP18000 would be a perfect choice, because it can provide 20V/3.5A. But I dont know if the Lenovo plug is inside the package. And it's expensive.
The "big circular plug" is 7.9 x 5.4 x 0.9mm plug for some other Lenovo machines, like Carbon X1. I never found an external power bank with "rectangular" y2p plug anyway.