A very simple 12v Battery pack. No circuit boards, no linear Voltage Regulators. Just a 12V sealed lead acid battery, a 12V Solar Panel, and a 5.5x2.1mm DC plug.

It works very well and is very big and much more expensive then the li-ion pack I put together. Some solar panels sometimes include a diode. The diode is used to keep from feeding power from the battery back into the panel at night. Just another note about diodes while they are great for keeping current flowing in one direction but they too consume a small amount of power. For this battery box the voltage is fixed so I can only use it on my 12v trail cameras. I would have to build another box for the 6v cameras or use a DC-DC buck (Step Down) converter circuit, or a Linear Voltage Regulator. The solar panel doesn’t have a high enough amps or high enough voltage to be worried about over charging the lead acid battery of this size. The lead acid battery can handle it. However Don't do this to a li-ion, their chemistry and they can't handle it and you will destroy a li-ion battery very quickly. You could use a solar charge controller but it would consume more power than your producing, and is over kill in this application. If you already have a 6v battery box, or you built a 6v battery box you use a DC-DC Boost (Step Up) converter circuit to increase your voltage to 12v for 12v trail cameras.

Lead Acid Battery Pack Cost
12v Sealed Lead Acid battery pack w/ Solar Panel
12v Solar Panel: $25
12v Battery: $20
5.5x2.1mm DC Plug: $??? (I reused a plug from an old broken adapter)
Plastic Ammo Box: $5
Total $50