Using Android tablet as spare battery for your phone - can this be done?

[Cloud]

I've been toying with the idea of using my old S7 as a spare battery for my S3.

When you plug in OTG devices they are powered from the host, so would this be possible with a modified cable?

Even just USB level charging would be a bonus

 

[Conack]

That's what I'm using my netbook for

 

[Cloud]

Thing is, the S7 doubles as a hotspot, so to carry that, a phone and a laptop / netbook around starts to defeat the purpose of being mobile

 

[The_Unbeliever]

Get a suitable solar charger.

 

[Cloud]

Get a suitable solar charger.

Any suggestions?