I made a power bank consists of 3 lithium ion battery 3.7v from an old phone battery.

2 batteries are in series and one is in parallel to grade up amp. The output is 7.4v thus the phone requires 5v for charging. I used an IC to convert that 7.4v to 5v.

Is it okay to charge the smart phone battery or will it damage or drain it?

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    \$\begingroup\$ "2 batteries are in series and one is in parallel". NOPE. Stop right there. You're going to damage your battery and your body. \$\endgroup\$ – Kevin Kruse Mar 1 '19 at 19:02
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    \$\begingroup\$ Instant death - of all batteries and possibly of the user. See Kevin's comment and the answer supplied. \$\endgroup\$ – Russell McMahon Mar 1 '19 at 21:09

Take the given comment seriously. Your text presents this circuit:

enter image description here

This is a perfect short circuit. If your batteries aren't fully lifeless, the fire will jump onto your hands, clothes and eyes as soon as you get it ready, no matter A and B are still disconnected.

Stop as long as you still can see!

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