- USB / DC / Solar Lithium Ion/Polymer charger - v1.0 ID: 390
USB/DC Lithium Polymer battery charger 5-12V - 3.7/4.2v cells ID: 280
USB LiIon/LiPoly charger - v1.2 ID: 259
The first one is explicitly for use with Solar panels, and having a higher product number I will guess it is a newer design. It has a different charger chip and that big cap. However it seems hard to keep in stock.
Can the 280 charger be used with your 6v solar panels?
What are the downsides if it is marginally usable?