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I wondered why my Anker PowerCore 20100 power bank would never charge from this solar charger, but would charge from a wall charger. So I performed some tests and found that if a cloud passes then the 20100 will drop to a trickle charge for the rest of the day. The 20100 dynamically reduces its charging current draw, but does not increase it. For example, if the sun is out the 20100 will charge at 2.0 Amps from this solar charger. If a cloud passes and the solar charger can only produce 0.25 Amps then the 20100 will reduce is current draw to 0.25 Amps (as it should). However when the sun comes back out the 20100 will still only draw 0.25 Amps, even though more than 2 Amps are available. This was verified using both the YZX Studio ZY1266 USB power monitor and the Drok Pocket Digital Multimeter. Anker support said the 20100 power bank was defective. I replaced it with a second one that behaved the same. I tested my older out of production Anker batteries: the Astro 3E also doesn't increase its charge rate, but the Gen 1 Astro E5 does. The E5 immediately responds when the sun comes back out and draws all available current from the solar charger. I again contacted Anker support and asked for a list of batteries that have been tested with and charge properly from the Anker solar charger. Anker could not produce anything so I was on my own. I purchased some other batteries to see what would work. The EasyAcc Monster 26000mAh Power Bank worked properly. Plus this battery has two charging ports so it can connect to both solar output ports and charge at greater than 2.0 Amps when enough sunlight is available. The Anker Astro E7 26800mah Power Bank works perfectly with the Anker solar charger. The RavPower 26800mah Power Bank works properly in almost all conditions with the Anker solar charger. However if the sunlight drops too low and the charger produces close to 0 ma, but then the sun comes out before the solar charger powers off, the RavPower would not charge anymore. None of the other batteries had this particular problem. I also have the ChoeTech 19W SunPower Solar Charger so I tried the RavPower with it and found that the ChoeTech will reset the USB connection within a few seconds of this happening. So the ChoeTech/RavPower combination works fine. But if you use the RavPower with the Anker solar charger you might come back to your battery at the end of the day to find it didn't charge.