V25 6,400mAh USB Always On Battery Backup Power Bank for iPhone, iPad, Samsung Galaxy, Android, and HTC Devices (Gray)

i've never been able to find a usb power bank that is always on and STAYS ON even after the device it's plugged into reaches full charge. because eventually your usb device starts dying again but most USB banks like this wont automatically kick back on and keep charging your devicethe BEST part of this is how it also functioms like an uninterruptable power supply for whatever you plus into it, protecting your USB from power outages. here's an example:I have a nice projection clock in the bedroom that ia powered by a USB wall plug. Everytime we received even the SLIGHTEST power hit on thw house (lightning, dropouts etc), the clock would reset to "12:00" and I had to set it again. ughbut with this nice little power bank (ans it really has a TON of mAh's for it's size, incredible), I can plug this power bank into wall power so it's always charging, THEN plug my USB clock radio into thia power bank, and now the clock radio is protected from power bumps and receives constant power. SO my clock radio now NEVER resets, even when we lose power for several minutes!this is unusual for portable power banks, most power banks stop sending power out their ports when you plug them in to charge them up. not this one, it can ALWAYS be used even when you're charging it upI had been looking for years for this. couldnt be happier with it.get this if you need a USB power bank that is always outputting power even while on charge itself, and one that's tiny with a lot of mAh's.kudos to the inventor. they should start marketing this as a "UPS for USB devices" because that's all I use it for and it works incredibly well and reliably for this!

If you are interested in something to carry around to recharge your cell phone or other portable, there are plenty of other power banks much cheaper than this that will do a great job. Skip this review and find one of those.My use case: make an Arduino-based toy that runs on batteries for portability, can be recharged with a standard USB charger, can be played with while recharging, and that restarts properly when the battery has been depleted and is then recharged.Power banks designed for cell phones don't work, because they come with a "feature" -- which is to shut off if the current drain has been low (thresholds vary) for a few minutes (times vary). The thinking here is that a diminished current demand means that the cell phone is fully charged.Unfortunately, microcontrollers are pretty efficient, and in my toy the Arduino drew about 70 mA. That's below the cutoff for standard power banks, so the toy would only stay "on" for a few minutes.I tried some other power banks that claimed to be "always on." Generally they needed a certain pattern of clicks on the on/off button to enter always on mode (which isn't possible when the pack is enclosed in a kid's toy) and, worse yet, once they're drained, recharging does *not* restart the output. The pack sits there waiting to be turned on again, by press of the unreachable button.I was about to give up when I finally found Voltaic. Their power banks meet all the requirements. "Always on" means there's always 5VDC at the output until it's exhausted, and the output recovers as soon as it's plugged in for a recharge -- which for an Arduino means it restarts its program, and all is well.Voltaic advertises that these are solar rechargeable, which I haven't tried. But that would be good for, say, a remote weather station.Compared to other power banks, this one costs the most per mAH, but as it ACTUALLY WORKS I'm happy to recommend it.

I was hesitant buying this after seeing a two star review of not charging with a dynamo bikepacking setup. But I was eager for a cache battery that I could charge while charging light bicycling electronics.Using a USB inline current and voltage monitor, once my 29er reaches 10 mph, my Sinewave Reactor is charging the V25 battery at 5V DC with approximately 600 mA. That works out to about 3W, which is what most dynamo hubs are rated for (6V AC, 3W). If I turn on my dynamo lights wired in parallel, then I can still can charge this battery at ~300 mA while having a dim running light.When climbing super slowly at 4 mph up a steep grade with lights off, the battery was still charging with 100 mA. That's an extreme low end but a testament that this battery will take whatever trickle is offered to it.Supplementing with a 6W solar panel (I found a cheap basic one that charges this battery around 1A at 5V) should lead to pretty decent electrical self-sufficiency, especially charging on a rest day or when off the saddle.I'm frequently riding offroad with forest canopy where solar is not helpful while riding. I can charge the battery 50% via dynamo on a typical long touring day and supplement solar for the rest charging devices at-will with stability.This battery is awesome. I wish I had it on past bicycle tours since its capacity is good for my needs, can charge and discharge simultaneously, fully charge small electronics without prematurely powering off, and fits in my frame pack with a short cable and plugged in without a strained connection.