Well solar panels are usually rate "unloaded". So if you don't plug anything into them then you'll get what they say. Which is great in magical PR spin world. But us mere mortals would like to use the product.
The 7 Watts advertised is in the real world about 1½ Watts if you use the inline "Voltage Controller". The "Voltage Controller" makes sure that the voltage, that you plug your expensive phone into, will stay at 5 volts (5 volts is the USB standard which is what charges your phone).
If you don't have the "Voltage Controller" inline then the raw output from the panels is there. So at midday in full sun, with the panels at the just the right angle you might get 6 to 7 volts. Which might not be good for you expensive phone. But there will be more watts for you to use to charge things. About 2½ Watts
The "Voltage Controller" needs some power to run itself (plus that little light on the side so you can feel good that it's working). And the cost for that is about a 1 watt. I didn't test what happens to the output of the "Voltage Controller" if the input is below 5 volts (like on cloudy day or in forest) will check that later. So like I said:
Charging a phone I'd leave the "Voltage Controller" inline. If you want to charge a battery and it can handle between 4V to 7V then remove the "Controller".
I did a quick test of the 23000mAH battery as I had forgot to do it
No you don't need 15V to charge it! It will try to charge down to 3.5V but the charging circuits won't start till around 6.5V. So to be safe I'd say from 7 volts up.
Here is another But. But I don't know if it will start charging when the battery is flat (below 25%) at less then 15 volts. I'll flatten it today and test that tonight.
Now I know that the battery is
NOT a 23AH (1000mA = 1A). Here is a picture of a 8.4 AH (8400mAH) 13.2 Volt LiFePo battery.
And it weighs 1 kg. So based on weight alone there is no way that there is a 23AH battery in the S23000.
Another got ya for the S23000 is the LiPo batteries in the thing. LiPos are very fussy things. They need very controlled, strict charging conditions. Do we remember all those Dell laptops catching fire???? If I know I not going to be using my LiPos (like the one in the picture) for a few weeks I will charge them in a "storage" state. I have a flash battery charger that will do that for me. And when I am going to use them I give them a proper charge the night before so they are ready to go. Storage charging will increase the life of the batteries.
In the S23000 there is nothing that smart for managing the batteries so I'd expect a useful life of about 1½ ~ 2 years before it won't hold a charge. Much like the batteries in your phones or laptops. They last for every when the things a new but after a few months.....
Here is some light reading on
LiPo batteries.
Daggo.