On the market we can find a lot of different types of batteries, they are made in different technologies and the same technology can be made in very different packages.
In this article we want to talk about lithium batteries in the 18650 package, a very common package commonly used

inside power banks, for example.

A lot of batteries made in this format don’t have an internal protection and to allow to use them to power up an electronic circuit in safety we must build an electronic protection around this battery.
What is an electronic battery protection?

it is a circuit that allow to protect your battery from, in the most case, this 5 possible events:

  • overcurrent discharge
  • overcurrent charge
  • overdischarge voltage
  • overcharge voltage
  • short circuit

overcurrent discharge
protect your battery and circuit from draining too much current from the battery.
If a battery source too much current continuously it will start to overheat and this can damage itself.

overcurrent charge
protect your battery from receiving too much current from a battery charger.
Like an overcurrent during a discharging, an overcurrent during charging can generate the same problems and damage the battery.

overdischarge voltage
protect your battery from reaching too low voltage value (for a liyhium battery typical minimum voltage value is 2.8V)
A lithium battery should have it voltage beetwen typically 2.8V to 4.2V (is some case 4.3V).
Exceeding these values, below or over the indicated thresholds, can seriously damage the battery.
the overdischarging voltage protection, protect the battery only when it reach the lowest threshold.

overcharge voltage
protect your battery from reaching too high voltage value (for a lithium battery typical high voltage value is 4.2V)
the overcharge voltage protection,  protect the battery only when it reach the highest threshold.

short circuit
Short circuit in a battery happens when + and – of the battery are linked togheter without any high resistance between them.
In this case a very high current is sink from the battery and the protection is usuful to avoid this to happen.

All these five features are manage by a specific IC together with other few components, like mosfet, to fully protect your battery.

In the next article I’ll talk about a circuit that works like battery holder and battery protection for 18650 package: Guard18650 based on BQ29700 battery protection, ECH8693R-TL-W that is a dual mosfet and DMP2006UFG-7, a P-mosfet to ensure an high quality reverse polarity protection.