Disclaimer: Im not an electrical engineer, Im happy to tinker and solder though.

So on a recent camping trip I had to keep charging the wifes iPhone using my USB battery pack.

I have the following components with which I want to make something I can charge devices (for 3-4 days) from;

- 1.5W Solar Battery Charger (has car battery clips)
- A 12V sealed lead acid (SLA) battery
- A USB battery pack (ie battery bank thing)
- A 12V to 5V micro USB adaptor (its a good quality hard wired one not a lighter plug adaptor)
- A 12V to 5V USB adaptor (ie lighter plug adaptor)

So I was thinking of either

1) Charging the SLA battery from the Solar Battery Charger and then connecting a 12V to 5V USB adaptor (lighter plug adaptor) when required to provide a powered USB port

Or

2) Connecting the Solar Battery Charger to the 12V to 5V micro USB adaptor which would plug into and charge the USB battery pack (it charges off micro USB). Devices could then charge off the USB battery pack

So really looking for best bang for buck. Would charging the SLA battery have more charges or would charging the USB battery pack via 5V down step be better.

Any help appreciated.