Originally Posted by CliffordK

Here is your CREE Extension Cord:
New Extensive Cable for CREE XM L T6 LED Headlamp Rechargeable Headlight FF | eBay

Your USB solar charger puts out about 5.5 V.
You need something that puts out greater than 8.4V.

You could wire two of those in series which would give you about 11V which would be somewhat closer than the 12V panels.

You might also consider a DC DC voltage converter. I'm not sure if the boost and buck converters are the same, but they would allow better tuning of your voltage output, and perhaps only requiring a single solar panel.

LM2596 Buck Step Down Power Converter Module DC 4 0 40 to 1 3 37V LED Voltmeter | eBay
DC DC 4 5 32V to 5 52v XL6009 Boost Step Up Module Power Supply LED Voltmeter | eBay

Oh, another calculation.
Your battery packs use four 18650 Lithium batteries.
4.2V, with 2 to 6 ah each. So, (qty 4) x (4.2v) x (4 ah) = 67.2 watt hours for full charge.

That USB charger puts out about 7W max, when pointed directly at the sun at noon (probably a bit optimistic). So, it would take at least 10 hours of peak power generation to recharge the battery from drained to full. I'd guess maybe a couple of days (which isn't too bad).