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I have two TP4056 modules (with protection circuit), which I am using to charge two batteries respectively, off a single power line. The modules are the ones that have charge output (B+/B-), and another regular output.

I'd like to be able to use both batteries (increased capacity) to power a single load, even while charging. The batteries are rechargeable 3.7V 16340 Li-ions, same make and capacity.

I'm not sure how to do this in a safe manner. I don't know if it would be safe to conjoin the outputs with this module, and I would like to avoid using diodes because of the voltage drop.

The question is: How can I make this work, in order to be able to use the device even while charging, and how can I connect the two batteries safely to the device in the first place?

My use case is described in the image. charging circuit

EDIT: Look to the comments for an answer regarding more than two cells. As the original question was for two cells, I had to choose one of two valid answers.

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Don't.

Just use one TP4056 and connect both cells in parallel.

This will work because Lithium cells have a wide voltage range. So when connected in parallel they will self-balance.

the TP4065 module includes over-discharge proteciton circuitry power should be takes from the out terminals of the TP4056 module, not directly from the battery.

Parallel connection

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  • \$\begingroup\$ Although there is a reduction in charge time to be considered (a single TP4056 is limited to 1A), I doubt my cells can benefit from more than 500-700mA per cell. I will likely choose this as the best answer after researching what you said about self-balance, unless someone gives me a scenario where I can use both TP4056 modules. \$\endgroup\$ – Mr.M Jan 31 '18 at 10:26
  • \$\begingroup\$ yeah, or maybe you can find a stronger charger module \$\endgroup\$ – Jasen Jan 31 '18 at 12:30
  • \$\begingroup\$ Works fine as long as one cell is not physically damaged, then it becomes a fire hazard unless fused \$\endgroup\$ – Sunnyskyguy EE75 Jan 31 '18 at 13:50
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    \$\begingroup\$ Active Protection IC is the smarter way to go. \$\endgroup\$ – Sunnyskyguy EE75 Jan 31 '18 at 16:27
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    \$\begingroup\$ I think so and the folks at addicore agree. But the thermal voltage characteristics are to raise cell voltage and lower ESR with rising self-heating, there might be a problem charging cold batteries with self-shorting. \$\endgroup\$ – Sunnyskyguy EE75 Feb 1 '18 at 11:15
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Solution

Be able to use both batteries (increased capacity) to power a single load with two TP4056 modules.

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    \$\begingroup\$ It would be much easier to interpret this is you used a proper switch symbol instead of a photograph. Are we supposed to guess the pinout? I can't even tell if your circuit is correct. Moreover, I really don't think the initial poster had a manual switch solution in mind. \$\endgroup\$ – dim Mar 3 at 22:06

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