The New Trent was recommended more often than others in this collection. My colleague Jason Perlow uses one on his business trips and had good things to say about it.

From the New Trent product page:

Quick Overview

• Charge Phones up to 6 times
• Portable iPhone Battery Pack
• Unrivaled Power & Speed - 12,000mAh Power
• Built to Last: 500x Charge Cycle Guarantee
• Dual USB: 2.1A and 1A
• Compact and Lightweight
• Compatible with Major Smartphones

The iCarrier can charge a phone and tablet at the same time with its dual USB ports. One is higher output than the other to charge bigger devices faster than a typical phone charger.

There is no pass-through capability so the iCarrier cannot charge devices while its internal battery is charging. Its 12,000 mAH capacity is twice that of the other products in this collection.

$76.95

The Mophie Juice Pack is a popular case for the iPhone with internal battery to extend phone usage. That case adds weight and bulk to the phone that many do not like.

Mophie also makes a separate portable charger that can be used to charge a tablet and phone at the same time. The Powerstation Duo has a 6,000 mAH with high output delivery for fast charging of tablets and phones.

From the Mophie product page:

• Dual-charging ports
• 2.1 amp charging output
• Built-in short circuit, overcharge protection
• 6,000 mAh battery

This charger does not have pass-through capability so it cannot be used to charge devices while charging its internal battery.

$99.95

The ZAGG folks are well-known for their iPad keyboards and cases, but they also have a line of portable battery packs.

The ZAGGsparq 6000 is a small pack with an integrated power plug, making it one of the smallest in this collection. 

From the ZAGG product page:

• Rechargeable lithium polymer backup battery
• Built-in prongs for convenient charging
• When plugged into an outlet, the ZAGGsparq works just like a wall charger (directly charging the device, then charging the internal battery)
• On/off switch to prevent battery drainage
• 2.1A output for ultra-fast charging, up to four times faster than a standard USB charger
• Universal charger powers all USB-charged mobile devices
• Charges iPad and other tablets at optimal speed

The ability to use the ZAGGsparc as a wall charger eliminates one or two power adapters from the travel bag.

$99.99

Belkin is famous for its mobile accesory product line and the Power Pack 4000. While this is not the most powerful in this group, it can deliver a fast charge to two devices.

According to the Belkin product page, the Power Pack has pass-through capability, meaning it can charge phones and tablets at the same time that it charges its internal battery. This means it can be used in place of a phone/tablet power adapter.

From the Belkin product page:

• 4000 mAh power for charging on the go
• Allows four full cell phone charges, two full smartphone charges or a full tablet boost
• Built-In Safety: Thermal Management, and Over-Current and Short Circuit Protections
• StorageSafe technology holds 95% charge up to 30 days
• Convenient charge indicator
• Two 6” USB to micro-USB cables for charging and recharging
• Wall adapter

$99.99

The TurboCharger is designed for international travelers and comes with cables and power plugs to work in many countries.

From the Proporta product page:

• USB TurboCharger 7000 mAH can charge anywhere and recharge anything. Standard USB input and output.
• Comes with two retractable cables and range of interchangeable connector heads including 1 x DS Lite, 1 x iPod, 1 x Nokia, 1 x Sony Ericsson, 1 x Micro USB, and 1 x Mini USB
• LED display shows level of charge.
• USB TurboCharger 7000 has an impressive 7,000 mAh storage — enough to recharge your phone, tablet, digital camera or gaming device several times.
• Includes World AC Power and Car Power Supply (with USB)

$79.95

The Enercell power pack can be found online and in some Radio Shack stores, so you may be able to check it out prior to buying one.

From the Radio Shack product page:

• Charge two devices simultaneously
• Output 1 5VDC/2.1A
• Output 2 5VDC/1A
• Runtime: up to 15 hours, depending on the device
• Battery charging time: 9 hours

$79.99