Nucleo PD "pass through" charging?

Is there a reference design/app note for "pass through" power delivery chargers/battery packs with these MCUs? IOW I'd like my design to do the following; 

-If connected to mains power/a small solar panel, charge the batteries while powering the load. 

-If disconnected from all other sources, power the load with battery only. 

For my own education I'd prefer X-NUCLEO-DRP1M1 but I'm willing to consider all options in that price range.

Obviously I cannot expect a small solar panel to supply enough power for the whole load, never mind for both charging and the load. So at best it will provide a little extra runtime. In contrast mains power should be sufficient for both.  

Battery is expected to be 4x18650 but I'm willing to consider other options. 

Many thanks in advance 

Joe.