Oldmill;
Getting the batteries free is good
.
The other side of the coin is what you already have available, or free or low cost.
A simple Solar panel setup with a inexpensive charge controller will go a very long way to what you ask.
Rich H and I used some of the very same sized batteries in our trip to the Philippines way back in 2010. We used smallish sized panels he found 10watt @12V and 17watt @12V.
The trick is to know how much energy you will need to store so you do not drain (kill the batteries) below 50%.
Since it doesn't look like you'll do heavy usage, then the 10 - 17watt panels should workout nicely.
DO NOT purchase the ones places like Harbor Freight and CostCo sells they just aren't work the $$$ for the wattage and limited life they have versus the size as well.
It would be best to grab the Amps labeled off each of the devices, add them all up, then add 20% more , then make sure you have enough battery to cover the max.
Let us know how you intend the recharge the batteries too.
Hope this helps
Bruce S