i.Sound says that the 8,000 mAh Power Max can fully charge an iPad while the 16,000 mAh can fully charge an iPad twice. After topping off the smaller Power Max we attached a fully discharged iPad 2 to it overnight. The next morning, the iPad 2 was 99 percent charged and the Power Max was depleted. Count that as a successful test.
Next we moved on to the larger-capacity Power Max. After an overnight charge, it had fully powered up our iPad 2. We then attached a second depleted iPad and let the Power Max charge it. On the second attempt, the Power Max gave our iPad only 90 percent, but considering there was no way to tell when exactly the first iPad had finished charging, we'll consider this successful as well.
The problem with testing this type of device is that it's tough to tell how the item will do in the long run, as portable chargers are notorious for losing their ability to hold a charge. During our three weeks of testing, we didn't notice the Power Max batteries lose anything.
The only slowdown in charging we did notice was when we attached multiple USB devices at once. Also, while it's great that these items can charge so many devices at once, the space between the USB ports is tiny. Any type of USB dongle with a larger frame will probably cover the port next to it--just something to keep in mind.
Overall we liked these portable power offerings from i.Sound. We can't yet judge how they stand up to long-term wear and tear, so we'll update this review accordingly if we encounter any bumps along the road. As for price, the Power Max rechargers seem to fall in line with other similar items, and can be found online for up to 30 percent off the original retail price.