I purchased an extra one of these batteries and am very satisfied with it. I never needed the backup battery, riding probably 10 miles a day with peddle assist on the bike. I used the USB charger on the battery to charge my phone while hunting (charged it fast), and it was a very useful feature. I never ran the battery below 4 bars on the indicator with all the riding I did and have also used it to power other 5 volt accessories for days. I never had a problem with this battery, even riding in the rain and extreme cold.
Great... a little heavy, but that is also great.