I want to charge mobile battery of 3.7 v directly by connecting 2 terminals of charger(5 v output) to two terminals of battery. My questions are

  2. what must be voltage adjusted to charge 3.7 v battery?
  3. Is there any circuit inside mobile phone charger already that will stop charging, when battery become fully charged?
  4. Is there any additional circuit required?
  5. Is there any risk/precaution ?

2 Answers 2


This is an absolute no-go.

  1. Not from the terminals on the outside of the battery, it is when you open up the battery-pack.
  2. Charging Li-ion batteries is mostly current controlled, with cell-temperature, voltage (change) and absolute charge as input parameters. A second (top-up) stage is voltage controlled.
  3. The battery should at al times being monitored against such actions or a defective charger, however the failsafe is not required to auto-reset.
  4. Yes, See 2.
  5. Yes, if you would succeed in direct charging the cells despite safety mechanisms an overcharge will even be able to cause an explosion.
  • \$\begingroup\$ A 3.7V battery on a 5V supply will draw a lot of current. If you don't have proper current limiting, that bug current causes heat inside the battery. A few years back (2006) Lithium batteries in laptops even caught fire: a Youtube search for "exploding batteries" is quite spectacular. \$\endgroup\$ Oct 23, 2014 at 9:58
  • \$\begingroup\$ As mentioned in #2 and #5. Li-ion batteries sometimes still give troubles as you can see in the grounding of all Boeing Dreamliners last year due to overheating batteries. :) \$\endgroup\$
    – Requist
    Oct 23, 2014 at 10:28
  • \$\begingroup\$ then how should i charge 3.7v mobile battery if i have mobile phone charger of 5v? is any additional ckt require? \$\endgroup\$ Oct 24, 2014 at 9:03
  • \$\begingroup\$ yes and depending on you electronic knowledge probably more then feasible for the result. Ckt depends on the battery, it already has some electronics inside, but this is different for every battery. The charger should communicate with the battery chip inside to determine how to charge (CC or CV stage). So you would need a bit of back-engineering to determine the circuit. But considering the effort, trow away what you have and rethink the question, what do you want to achieve in the end? \$\endgroup\$
    – Requist
    Oct 25, 2014 at 10:18

Your 5v charger can directly charge the battery by using on- board terminals of battery but battery may explode if you do not attend to it often! If battery is purely original,u may not have to worry much because quality batteries do have protection circuit boards which MAY prevent swell or explosion,... otherwise... So 1:it is possible . 2:Any voltage over 4 and less 5 (for safety reasons) 3:No . 4:yes . 5:yes

  • 1
    \$\begingroup\$ This answer is dangerously incorrect, for the reasons outlined by Requist. \$\endgroup\$
    – user39382
    Mar 31, 2018 at 7:25
  • 1
    \$\begingroup\$ Very poor and incorrect \$\endgroup\$
    – CNA
    Mar 31, 2018 at 9:33

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