# How can I use two TP4056 with two li-ion batteries, but single load?

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.

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.

Don't.

Just use one TP4056 and connect both cells in parallel after balancing them first. Don't connect batteries with more than 0.2V difference in parallel as this can risk fire and explosions (excessive charging current from one to another).

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 protection circuitry power should be taken from the out terminals of the TP4056 module, not directly from the battery.

• 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. – Mr.M Jan 31 '18 at 10:26
• yeah, or maybe you can find a stronger charger module – Jasen Jan 31 '18 at 12:30
• Works fine as long as one cell is not physically damaged, then it becomes a fire hazard unless fused – Tony Stewart Sunnyskyguy EE75 Jan 31 '18 at 13:50
• Active Protection IC is the smarter way to go. – Tony Stewart Sunnyskyguy EE75 Jan 31 '18 at 16:27
• 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. – Tony Stewart Sunnyskyguy EE75 Feb 1 '18 at 11:15

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

• 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. – dim Mar 3 '19 at 22:06