Just Mobile has been making beautiful, widely-admired Apple device-focused batteries for years — Gum, Gum Plus, and Gum Max just to name a few — so its version refreshes have tended to be somewhat predictable: tweak the capacity, improve the power output a little, and bump the price. Thus, the $40 2008 0.5-Amp version of Gum became the $50 2012 1-Amp Gum, the $70 2009 1-Amp Gum Plus became the $80 2012 2.1-Amp Gum Plus, and now the prior top-of-the-line $110 2011 2.1-Amp Gum Max has a sequel: Gum Max Duo ($130). Nearly identical to its predecessor in design, Gum Max Duo has once again been improved to appeal to past and new users, though as the price has jumped up further, it’s now precariously close to being impractically expensive for its intended purpose.
The big changes to Gum Max Duo can be summed up simply: start with late 2011’s silver aluminum and black plastic 10,400mAh model with 2.1-Amp power, which measured 4.3” by 3.2” by 1.1”. Replace the battery with a 11,200mAh version, and up the rated output speed to 2.4 Amps, which is supposedly enough to refuel even Retina iPads at their peak speeds, as well as supporting the top recharge speeds of all other recent iPad, iPhone, and iPod models. Add a second full-sized USB output port to the right side, and keep everything but the rear text looking the same. That’s pretty much it—except for tweaks that you might or might not consider major.
One such change that we really liked is the replacement of Gum Max’s cloth drawstring carrying bag with a decidedly superior ruggedizing solution: a form-fitting rubber sleeve with a handsome, Bauhaus-evoking design. Rather than tossing Gum Max Duo into the same bag with its cables and giving it the opportunity to scuff—something that has happened over time to our prior Gum Max review unit—the rubber sleeve now covers all of the battery save for its USB ports, while letting you access the front power button and always see the line of eight yellow LEDs that indicate current charge status. Just Mobile’s included sleeve is black, with classic yellow, blue, and red options available separately for $9-$13 each depending on whether you use a coupon in the Gum Max Duo package.
The yellow LEDs are notably visible even in the yellow sleeve.
Beyond swapping the bag for the sleeve, it’s worth noting that Gum Max Duo loses one pack-in relative to the original model—an Apple device-specific cable. The 2011 and 2012 versions of Gum, Gum Plus, and Gum Max all included an Apple Dock Connector cable, but with the transition to Lightning still underway—and dicey for developers—Just Mobile doesn’t include either Dock Connector or Lightning cables in the package. You still get the USB to Micro-USB cable needed to recharge the battery—and because of the high capacity, that remains a lengthy process that you’ll probably want to use a self-supplied wall adapter or very recent model Mac to achieve. Given the high price tag, it’s a shame that Gum Max Duo doesn’t include its own wall charger or Apple device cable; dreamGear’s i.Sound Portable Power Max includes a wall adapter and an even higher battery capacity, though it’s physically much larger and less premium-feeling.
Two things about Gum Max Duo’s design are really nice. The LEDs remain on while the battery is discharging, which may use a bit of power but clearly indicates the current energy level—useful when monitoring the longevity of a high-capacity cell. On a related note, Just Mobile has also recessed the power button, which works simply for “on” and “off” purposes rather than including a “tap to see the current power level” feature. Because the button’s recessed, it’s harder to accidentally depress unless the rubber sleeve is on, which makes the button just a hair higher than the rest of the sleeve’s top surface. Ideally, the button would be a little concave in any position to avoid mistaken activation.
Gum Max Duo’s power performance is mixed but generally positive.
The good news: it offers a little more power than the original Gum Max, and is capable of delivering around 75% of a full recharge to a Retina third- or fourth-generation iPad. One of our tests hit 75% with the latest iPad, and another hit 76%, which is slightly above Just Mobile’s promised extra 7 hours of iPad run time. Needless to say, because earlier iPads and the iPad mini have much smaller batteries, you can expect to get more than a full recharge from Gum Max Duo—approximately 115% with the iPad or iPad 2, and perhaps two recharges of the iPad mini. While the 11,200mAh cell inside Gum Max Duo isn’t the largest we’ve ever seen in an iPad battery pack, it’s right up there.
The less impressive news is on the time and status indicator front. Despite its billing, Gum Max Duo’s “2.4-Amp” port isn’t as fast as the 2.4-Amp wall chargers we’ve tested—we commonly saw recharge times in excess of five hours just to reach the 75% mark, even though 100% Retina iPad wall recharges from Apple’s 12W USB Power Adapter take around the same amount of time. Interestingly, Just Mobile’s second USB port is labeled “1-Amp,” yet also took 5 hours and 15 minutes to provide a 76% charge. Our impression is that the labeling only suggests how power will be supplied in the event that both ports are in use at the same time, sharing the battery; otherwise, either can operate at a speed that’s closer to 2.1 than 2.4 Amps.
Additionally, Gum Max Duo’s status indicator lights aren’t entirely linear to let you know how much the internal battery has recharged or discharged. All eight of the lights go solid when you’ve finished recharging Gum Max Duo, a lengthy process given the big cell.