Amazon has a Jackery Jewel iPhone charging cable with a built-in 450 mAh battery. Price is $17, and code JKRJEWEL takes $3 off. Amazon states the weight is 1.28 oz; I do not know if this is accurate.
450 mAh isn’t much, of course, but this might be useful if you use a solar panel. On the iPhone at least, the screen comes on momentarily when charging restarts, so if the sun exposure is spotty, you may drain more of the battery than you charge from sun. Having a small battery inline with the charging cable should provide a nice buffer to prevent these on/off cycles.
I have no experience nor affiliation with this product, but I thought it interesting and wanted to share the deal.
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