I am planning to make automatic rechargable emergency led light (automatically lights up when there is a powercut). I scavenged led's from old emergency light. I planned on using this 3.7V 300 mAh battery . The circuit automatically goes to charging mode when there is power and switches to battery when power is off. Can anyone please clear these points for me?

  1. Can I use my mobile charger which is rated 5V 1A output for charging it.
  2. If so, the circuit is turned on 24/7, the battery seems to have overcharge and overdrain protection circuit. Will the battery last if the circuit is always on?

You need a LiPo battery charger. Connecting the battery directly to the phone charger will if you're lucky do nothing. If you're unlucky it will make your battery do an impression of a Samsung Note 7.

A phone charger is very inaccurately named, all it does is supply a constant 5V. All of the intelligence in how to charge the battery is built into the phone itself.

  • \$\begingroup\$ Haha that seems to create another emergency . If I have an Li-Po battery charger can I keep charging it 24/7 as the battery seems to have inbuilt overcharge protection. Thank you :D. \$\endgroup\$ – Teja Allani Oct 27 '16 at 12:23
  • \$\begingroup\$ A Li-Po charger (or Li-ion, a think the charge profiles are the same for both) will automatically shut off once the battery is fully charged, if the voltage then drops below a certain threshold (generally it won't, the batteries hold charge very well) the charger will start up again and top the battery up. Normally all the overcharge protection does is that if you supply a voltage over a certain level the pack disconnects the battery cells from the outside world. The in battery protection is purely for charger faults and should never be needed under normal operation. \$\endgroup\$ – Andrew Oct 27 '16 at 13:23

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