Buy these (*only* in black, for price) for their pass-through charging! nest cams, etc., can use them.
Quick summary: * not recommended except as mentioned below, but 5 stars for recommended use * super cheap pass-through charging (most batteries don't have this) for ~$6 each outweighs quality concerns (buy 2) * nice build quality (metal case), but other reviews suggest quality issues with longevity * use to automatically keep usb cameras on during a power outage * buy black; all other colors are way too pricey for what this provides * i bought six (using my account and my wife's) for several dropcams because these are such a deal details: the outstanding deal here is the black charger, and that's the one i'm giving five stars (it's about a third of the cost of the other colors and is otherwise identical to them). there are concerns about quality (see numerous other reviews), but the black chargers are, as of this writing, hovering around $6 each. i bought mine at $8.50, and i'm still happy. why? because these have pass-through charging, which means you can plug them into a charger and then something into them, and they'll charge themselves while providing power to the device plugged into them. this is *outstanding* for this price point. while i don't normally recommend low-capacity batteries, and while there are quality concerns about these (again, see the other reviews), it's essentially impossible to find pass-through charging at this price, and thus i *highly* recommend these for devices like nest cams which plug into a usb power adapter to run. plug one of those into one of these *first*, then plug *this* into the power adapter, and voila: your device will weather a power outage of many hours without a problem (note: make sure your wifi router and network equipment are plugged into a ups so they, too, will stay on). the led is *very* bright, so cover it with electrical tape if you will use it in an area that will otherwise be dark. the quality concerns mentioned in the reviews might be an issue, but, hey, they're $6 each. buy 2-3 - amazon will only let you get 3 per account, it seems, if you're buying the black ones. the included photo shows several of them daisy-chained together. i've got 6 total, and i'm putting 2 on each dropcam i own. i'm hoping, even with the reported quality issues, no more than one of those two will fail per camera. edit: nope, one per camera. i'd forgotten to edit this, and please see the comments for why it's a bad idea to chain the batteries.