I bought the PowerGen PGMPP90000 battery pack because I was taking part in a 100k walk that would take 24hours+ and I wanted to use my phone to track my progress. From practice walks, I knew I'd need to charge my phone a number of times throughout the walk to enable me to track my progress for the whole 24hours.
I've had external batteries before and they've never really lived up to expectations, but this one is fantastic. Every 5 hours or so, I was charging my S3 from about 25% back up to fully charged in around 90mins (I found turning off data massively reduced the time needed to recharge). By the time I finished my walk (26hours), I still had sufficient charge left in the PowerGen to re-charge my phone once more whilst I sorted myself out before making my way home. After that, I reckon there was still sufficient charge to do one final re-charge before it would have been fully exhausted.
I only needed the in-built short USB cable, but it comes with a variety of other connections for most modern phones and two other full-size USB sockets to charge more than one thing at a time. The light is an added extra that I didn't need and twice I found the light had been turned on by mistake (pressing against something in my pack), but operation is simple and easy even when sleep deprived at the end of a long walk! Having both the battery pack and my phone in my trouser pocket was not a problem - it just isn't that heavy.
Altogether, a great product. It simply did exactly what I needed - fast charging with capacity to re-charge a phone like the S3 again and again whilst being used with GPS apps like MayMyWalk.
This isn't a long-term test, I bought it specifically for this event, but already, it's been worth every penny.
Tip: For the fastest phone re-charge, turn off data. At one point, even though I had the battery pack plugged in to the phone, the phone was clearly draining too much power from the battery to make any difference to the level of charge in the battery - was out in the countryside with very little signal. I initially stopped a number of apps like Facebook, Google Maps amongst others, but eventually turned data off altogether. Once I'd done that, the battery was recharged very quickly.