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The 4000 mAh ASUS ZenPower Slim Power Bank (ABTU015) is a very slim, compact and stylish device for charging your smartphone or other mobile devices on the go from Asus. The 4000 mAh battery is inside a plastic case with a larger matte and smaller glossy surface and that looks pretty nice, however the glossy plastic scratches very easy when touched and very soon it does not look that good anymore. The device also has a single white LED disode that provides “flashlight” functionality that in our opinion is totally useless and the power bank could’ve been better without it anyway. There is an on/off button (used for the flashlight as well) and a small three-LED indicator about the current power bank charge that looks nice and is quite useful. The compact size and weight make the ASUS ZenPower Slim Power Bank perfect to sit in your pocket and save you whenever you need some extra power and cannot use a power charger for your smartphone or other mobile USB gadget and without the glossy plastic part and the LED light it could’ve been a really great small capacity power bank. Do note that ASUS also offers a version of this portable power bank with a smaller 3000 mAh capacity that is apparently with the same specifications as the 4000 mAh version we are testing here, apart from the 1000 mAh lower capacity battery inside it of course.

4000 mAh ASUS ZenPower Slim Power Bank Specifications:
– Battery Type: Rechargeable Li-Polymer Cell
– Battery Capacity: 3.85V/4000 mAh
– Input Power: 5V/1A
– Output Power: 5.1A/1A
– Rating Capacity: 5.1V/2200mAh
– Charging Time: <6 hours with DV 5V/1A standard cable - Dimensions: 115 x 71 x 8.3 mm - Weight: 92 g

We need to see how well the ASUS ZenPower Slim Power Bank manages to perform under our test conditions with a constant current load of 1.0A as per its official rating in order to get a better idea on what to expect in terms of actual usable capacity. In the official specifications Asus rates the useful capacity at 2200 mAh. This was something that we were actually a bit surprised to see mentioned in the official specifications for a power bank as usually manufacturers do not cite these cumbers in their product’s specs. The 2200 mAh rating sounds a bit disappointing for a 4000 mAh battery inside the power bank, but our tests have shown that you will actually be getting more… We managed to get 2574 mAh or 12.11 Wh as usable capacity and that is actually what we consider a very good performance, though the output voltage was a bit lower at about 4.7V, but keeping stable at that value. So good job for Asus for this power bank, but it could’ve been even better without the extra glossiness that easily scratches and the useless LED light “flashlight”.

The performance of the 4000 mAh ASUS ZenPower Slim Power Bank in our tests:

– 2574 mAh at 1.0A load

– 12.11 Wh at 1.0A load