I've seen a number of videos on YouTube where people have built a "Power Box" by putting a 12V deep cycle battery in some kind of weatherproof box with a charging equipment and added various switches and ports on the outside.
https://www.youtube.com/results?search_query=powerbox
I'm looking into building one of these for my annual camping trip in the desert, and was considering using this for a battery:
Mighty Max Battery 12V 22AH SLA Battery
Volume: 7.13" x 3.01" x 6.57" = 141 in^3
Energy Density: 22 AH / 141 in^3 = 0.15 AH/in^3
Weight: 13.1 lb
Price: $44.99
However, I also already own a number of Anker PowerCore Li-Ion based USB power packs like this. Which have nearly the same AH rating.
Portable Charger Anker PowerCore 20100mAh
Volume: 6.5" x 2.3" x 0.9" = 13.5 in^3
Energy Density: 20.1 AH / 13.5 in^3 = 1.49 AH/in^3
Weight: 12.56 oz = 0.785 lb
Price: $45.99
Both of these batteries are about the same price and hold about the same number of AH. Yet the USB battery pack is significantly smaller, lighter, and more energy dense.
If I don't have any need for 12V power, and only need 5V/USB power to charge my camera, cell phone, and run some LED lights. Is there any point to even considering using a 12V SLA battery?
Best Answer
...hold about the same number of AH
But there's the catch! A big one:
The mAh rating for the SLA battery is at 12 V so that equates to:
12 V * 22 Ah = 264 Whr (Watt*hour).
But for the powerbank it usually is at 3.7 V (the nominal voltage of a Li-Ion based cell), almost all powerbanks use a 3.7 V battery and a DCDC boostconverter to make the 5 V output. The manufacturers want to advertise with a large numger of mAh so they use the actual battery capacity but "forget" to tell you that that number is at 3.7 V and not 5 V.
So at 5 V you will not get 20.1 Ah but (ideal maximum) 3.7 V/5 V * 20.1 Ah = 14.9 Ah. That exclude the losses of the 3.7 V to 5 V conversion. But it gets worse, the actual energy stored is:
3.7 V * 20.1 Ah = 74.4 Whr
So the SLA battery has about 3.5 times more energy than the powerbank.
So your assumption that the same mAh rating means they also contain the same amount of energy is false!
Combined with an efficient DCDC converter to convert 12 V into 5 V my guess is that the SLA battery can easily charge a phone at least 4 times more than the power bank. In practice that 4 times might even be conservative as down conversion (12 V to 5 V) is generally more efficient than upconverting (3.7 V to 5 V).