This thing worked GREAT….I highly recommend. If I can make it jump start a car, then anyone can do it.

This thing worked GREAT….I highly recommend. If I can make it jump start a car, then anyone can do it.  Read Less

I received this item a few days ago. So far I have checked the USB charging function and voltage output of the jumping function...  Read More

I received this item a few days ago. So far I have checked the USB charging function and voltage output of the jumping function. The USB charger seems to work fine, and the jump function seems to have been implemented by wiring either three Li-Poly or Li-Ion batteries in series, for a combined nominal voltage of 11.1V, and a combined maximum voltage of 12.6V. If each of the 3 Li-Poly battery cells is 4000 mAh, this should easily be able to provide enough sustained current to start a completely dead car (although I have not yet tested that function -- EDIT -- tested below, works). I will add additional sections to this review as I continue to test the unit (each charge and discharge cycle takes hours, so the review will trickle in as I am able to run cycles).UPDATE 1: A better user manualThe user manual that comes with this product is lacking, so I'll post a few notes here:1) The jump start function is always on. Just plug in the cable and clamp to your battery to use.2) To use the USB charger, turn the switch to 'on' and press the power button once. If no current is drawn from the USB port, the unit will time out and shut down.3) To use the laptop charger, turn the switch to 'on' and press the power button once. Press additional times to cycle through the voltage, until the voltage indicated by your laptop's OEM charger is illuminated. Then plug in your laptop. DO NOT, I repeat, DO NOT plug in your laptop with the incorrect voltage selected, as this may cause permanent damage to your laptop.4) To use the police strobe lights, turn the switch to 'on' and double click the power button. Double click again to turn it back off.4) To use the police strobe lights, turn the switch to 'on' and long press the power button. Additional clicks of the power button cycle BOTH the light mode and laptop voltage, so don't press it with your laptop plugged in. Long press again to turn off.UPDATE 2: USB Charging FunctionalityI have run a capacity test by fully charging the unit, and then fully discharging via the USB port using a USB load simulator and a USB multimeter to measure discharged capacity. I discharged the unit at 2.0A; at this current the unit's output was 4.95V, which is well within the USB specification ... so it easily meets it's claim of 2.0A USB charging. I should note, though, that many '2.0A charger actually raise the voltage *above* spec during high rate charging to compensate for voltage drop in the cable. This unit does not do that, but neither does the other 'jump pack' that I have, so it's probably not something that they bother with in a device whose primary function is not charging. The net effect is that if you want to actually achieve 2.0A charging with this, you will need both a relatively heavy and short USB cable so that you provide the charging device with the maximum possible voltage.As far as the actual capacity of this pack is concerned, it also seems to meet its claim of 12,000 mAh. Before I delve into why I say seems to meet its rated capacity (instead of definitely meets), there is a bit of background information that is necessary to understand the nuances of how voltage, losses, and efficiency affect the measurement process -- the short version is that it's impossible to nail down the exact capacity of a device without tearing it apart to get direct access to the internal batteries, so you're limited to measuring power actually delivered & estimating internal battery capacity based on that.You can think of voltage as the similar to the 'pressure' in a water hose. The power delivered by a device is really equal to Voltage * Current (where current is like the 'flow' in a hose). Whereas all standard USB powered peripherals (including phone chargers) operate at 5V (except for the newer quick charge tech), Lithium Ion and Lithium Polymer batteries have a nominal voltage of only 3.7V (they start off at about 4.2V, and work down to about 3.3V when dead). To feed your devices the 5V they expect, every portable power bank, jump starter, etc -- any type of battery powered charger -- must convert its internal 3.3-4.2V voltage to a constant 5.0V for use by your devices. This has two effects:1) There is an efficiency loss in the conversion circuitry, so a 12,000 mAh power bank will actually not be able to charge a 3000 mAh phone four times as intuition might predict. If you've noticed that chargers get warm while charging your device, that heat is being generated by power from their battery that is lost in the internal circuitry, and it reduces the amount that's actually available for charging. While some chargers may be more efficient than others, it's impossible to make a 100% efficient conversion circuit and ALL chargers of this type will have some loss.2) mAh (milli amp-hours) are a terrible way to measure a product's capacity, because really they do not measure the power delivered but only the current that has flowed, ignoring voltage (and remember -- power is current TIMES voltage, so voltage matters!). Since all power banks, cell phone batteries, etc. capacities are rated using the 3.7V nominal voltage of Lithium Ion batteries, if you are measuring charge current at the 5.0V USB voltage, you have to do a conversion (which I'll do for you below) to get the capacity at 3.7V. This is why the power company measures using watt-hours instead amp-hours: watt-hours account for the voltage AND current, and provide a true measure of power.Having said that, I measured 6355 mAh on the USB port from a full charge to completely dead. Converting from 4.95V (the voltage that was being output by the pack) to 3.7V, I get a measured usable capacity of 8502mAh (6355*4.95/3.7). Since this product is rated at 12,000 mAh, that means that the voltage conversion efficiency is about 71%, which seems to be about average for mobile power banks.So, my conclusions w/ regard to capacity are:- This really is a 12,000 mAh battery (many sellers lie about capacity -- not so GeekPro! Nice to see an honest seller)- The USB conversion efficiency is about average, perhaps a bit below, at 71%.UPDATE 3: Jumping functionalityThe current produced by using this as a jump starter is too high for any of my equipment to measure, so I can only relate an anecdotal experience. I finally had the opportunity to try this on a dead vehicle today -- my Dad's V10 Ford Excursion. He called me and let me know he had a dead car (I've been waiting to test this), so I drove over to his house to give it a shot. Now I did feel a little stupid hooking a jump pack the size of a VHS tape to a vehicle with a 6.8L V10 (my Dad commented there's no way that's going to work ... aren't you worried you're going to hurt your gadget?), but I tried it anyway ... for science. The result was actually better than I expected -- Although there wasn't enough power when turning the key *immediately* after connecting the jump pack to start the engine, after a ~20 second wait to let the battery get a bit of charge the truck started right up. I'm extremely pleased with this performance, since I now have confidence that it will start basically anything I connect it to.NOTE: GeekPro provided this product to me at a discount for review purposes. My final review will consist of unbiased, measured, objective information that cannot be influenced in any way by GeekPro (besides making and/or not making a product that measures up to its claims :).  Read Less