I've experimented with several of these class of device. They are a 3.7V Lithium battery with a charging and discharging circuit attached.
Like the high current power adapters, the outputs are not always 5V; sometimes they are somewhat higher, so that at high current charging the voltage at the other end of the cable remains good for the smartphone or tablet. I wouldn't let them near any USB HDD until I'd checked the voltage and ripple; to avoid harm to the input regulators on the USB HDD. Some of them cannot be charged at the same time they are being discharged, so they are useless as a DC UPS. Some of them continuously run the discharging circuit, so they lose capacity rapidly after being charged. This is because they don't detect the USB plug, or don't have a power switch. Their end to end efficiency isn't great. Because they are being sold by capacity, more of the battery capacity is used. The cycle life seems to be around 1000 full charges, about half what would be expected from a product that optimises for lifetime. -- James Cameron http://quozl.linux.org.au/ _______________________________________________ Server-devel mailing list Server-devel@lists.laptop.org http://lists.laptop.org/listinfo/server-devel
