I have three devices, Nobis nb7022 s, droid mini, asus memo pad 7 (me170cx). I am using a charger that has a rated out put of 2000ma. The nobis draws 8 to 10 watts from the wall outlet. the droid mini and asus can only pull 3 watts from the same charger and cord. the asus is only a few weeks old while the droid and nobis are a about a year old.

What is the reason for the difference in power draw? the droid came with a 2 amp charger. Is there anything I can do to make the droid and asus draw more power and charge faster?

Additional information:

I believe the problem may be that the Droid Mini and Asus may think they are connected to a computer.

  • Are all devices capable of the same Quick Charge technology? USB Quick chargers communicate with a device to allow 2 Amps of output.
    – GiantTree
    Commented Dec 12, 2015 at 11:40
  • I don't believe any of them have quick charge technology, but the droid mini came with an adaptor that is rated at 2 amp output. I'm using the charger for the droid mini for this test.
    – Chris
    Commented Dec 13, 2015 at 21:40
  • It's certainly possible that the Droid uses proprietary technology that is incompatible with the others.
    – GiantTree
    Commented Dec 13, 2015 at 21:46
  • It's a droid charger so if it is proprietary, I expect it to charge the droid faster than the Nobis tablet I paid 40 dollars for a year ago. I have tried other chargers and cables with the same results.
    – Chris
    Commented Dec 13, 2015 at 22:46

1 Answer 1


Short Answer

  1. Devices mentioned have different battery capacities. They are meant to be charged with different rated current and therefore different power ( Asus device is 3950 mAh, Nobis is 2500 mAh, Droid Mini 2130 mAh capacity).

  2. OEM proprietary charging methodology can also significantly vary current. For instance, Note 2 charging current is 1600 mAh while Xperia charging current is around 600 mAh for similar size battery

  3. You can force higher current for faster charging but not advisable (unless OEM offers a way)

  4. What you can do to ensure rated current is delivered is covered

Long Answer

I do not know how you are measuring power in watts directly , but power is given by this equation (ignoring power factor or efficiency of charging)

P (Watts) = Voltage (Volts) x Current (Amps) (or corresponding milli units)

Reasons for difference in power drawn

Voltage supplied by a standard USB wall charger is 5V. That leaves us only current to be varied to obtain varying power

  1. Typically, current drawn by the charger is dependent on

a) Charging Rate Charging rate is a measure that governs at what current a battery is charged and discharged. At 1C, a battery rated 1,000mAh charges at a current of 1,000mAh. In an ideal world the battery would be fully charged in 60 minutes. At 1C, the same battery discharges at 1,000mA. Ideal charging rate is accepted to be around 0.5 to ,0.8 C for maximum battery life (battery life is measured in discharge cycles). This rate is decided by the OEM and coded in the charging algorithm implanted on ROM and varies

b) Battery Capacity (mAh) or size as commonly referred. Charging rate is varied dependent on this by OEM. Battery capacity of your Asus device is 3950 mAh, Nobis is 2500 mAh, Droid Mini 2130 mAh

c) Battery Type Not really relevant since most mobile devices and tablets use Li-Ion or Li-Po batteries

  1. Li-Ion or Li-Po charging When you charge a battery at charging rate decided by OEM, it goes through four stages of charging (Constant Current Charge,Saturation Charge and Ready No Current and Ready), see Figure 1 of BU-409 Charging Li-Ion. As you can see from graph voltage and current vary so if you are measuring current using an app like Ampere and derive wattage from current reading, you could end up in wrong comparison if you are not measuring in the same stage of charging

  2. OEM proprietary charging methodology can also significantly vary current. For instance, Note 2 charging current is 1600 mAh while Xperia charging current is around 600 mAh for similar size battery

You are comparing Power between Asus (3950 mAh), Nobis (2500 mAh), Droid Mini (2130 mAh), which by itself is not an apple to apple comparison and in conjunction with factors above

Droid and Asus power drawn is similar owing to capacity of battery being similar, whereas Nobis capacity is nearly double compared to Droid,so it seems fine and there is no need to "force" more current to be drawn. Doing so will result in poor battery performance. Simply put, forcing the battery to charge faster by increasing the current will result in a battery that discharges faster. This is covered in my answer and in the Battery University link above

However, to answer your question

How do I increase power drawn?

  1. Using apps from play store which claim to charge faster

  2. Using "fast chargers"

  3. By flashing a kernel which permit you to alter charging current, if your device is rooted

** I do not recommend options 1 and 2 for reasons mentioned in my answer. Option 3 is safer by comparison but needs to be cautiously tweaked and you need to understand the risks.

How to ensure getting maximum (rated) current

  1. Don't use power intensive apps while charging. Reasons

  2. Get the right combination of chargers and charging cables by measuring current with Ampere or 3C Battery Monitor Widget to rule out charger cable problems resulting in low charging current.

  3. If you are replacing charger cable, go in for a shorter thicker cable (24/ 28 awg) rather than longer, thinner cables as the former offer less resistance to current

  4. Cleaning the charging port of your device by blow drying it to dislodge lint or dirt that does accumulate when your phone is in pocket or outdoor usage (they cause poor connection and increase resistance )

  • Thank you for taking the time to assemble such an informative response. I understand how to manually charge batteries, but I think this will be very helpful for others.
    – Chris
    Commented Dec 13, 2015 at 21:50
  • I am measuring the power directly at the wall. So I'm not actually measuring the charge rate of the batteries. My droid mini came with a 2 amp charger, but the charger doesn't come close to drawing 2 amps.<br>"You are comparing Power between Asus (3950 mAh), Nobis (2500 mAh), Droid Mini (2130 mAh), "<br> Well, the droid mini and asus draw the same wattage, but the nobis draws 3 times as much. Based on your post this shouldn't be.
    – Chris
    Commented Dec 13, 2015 at 22:02
  • See your point but an important factor is how the manufacture has decided on charging algorithm. For instance between Note 2 and Xperia both having 3100 or nearly same battery, charging current for Xperia is around 600 and for Note 2 around 1600mAh. also on What stage of charging are you measuring, constant current or constant voltage. This was pointed out as a possible reason for variation
    – beeshyams
    Commented Dec 13, 2015 at 22:13
  • Similarly the charging current between Honor 4 and Note2. The former has charging current higher despite having a smaller battery. Yes, this point should have been added in reasons for variation and thanks for pointing that out..Will edit answer
    – beeshyams
    Commented Dec 13, 2015 at 22:19
  • I'm not sure what charge stage the batteries are technically using. I have monitored the devices at different battery percentages, approximately 30%, 60%, and 90%. Only the Nobis varies on how many watts are drawn from the wall outlet, but that variation isn't percentage dependent (it seems to tend to draw more watts when being heavily used. The droid and ASUS don't seem to vary even if turned off. I am using a "kill a watts ez" to measure.
    – Chris
    Commented Dec 13, 2015 at 22:34

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