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I have a handful of lithium-ion batteries with very low capacities, the lowest being about 700mAh, which I wish to connect to a charging module to avoid having to physically take out of my device/project to recharge. I only have access to cheap Chinese TP4056 USB charging modules on eBay, which provide 1A current, which I have heard is dangerous to batteries smaller than that. The TP4056 modules also have 5 volts for both input and output, which is necessary for my application. How will I limit or reduce the current, if possible, to avoid damage or catastrophic failure of the battery? Is it possible to do so without lowering the voltage? Is it safe to charge these batteries at 1A? I have been unable to find any modules that go below 1A, and Adafruit/Sparkfun/Mouser etc are not accessible in my country.

The battery's device will be charged through USB and require 5V, which the TP4056 boards provide. It seems to be similar to those DIY 18650 USB power bank kits.

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TP4056 datasheet

On page 3, there is a table listing values for Rprog, connected to pin 2 of the IC. All you have to do is unsolder Rprog and replace it to get a different charge current limit.

(Those modules look rather handy, especially at 10x for $3)

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  • \$\begingroup\$ From memory the ones more common and available in larger quantities only have the battery output, not the 5V. But anyway, I see how the output can be changed by the resistor value, but it's a tiny SMD part. Is it even possible to change that? \$\endgroup\$ – i9010tr Jul 13 '16 at 16:40
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    \$\begingroup\$ You don't have to change the smd resistor. Just cut the track going to pin 2, and solder an axial resistor from pin 2 to Ground. Set charging current to the lowest value that still gives an acceptable charge time (eg. 350mA will charge a 700mAh cell in ~2 hours). \$\endgroup\$ – Bruce Abbott Jul 13 '16 at 18:23
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    \$\begingroup\$ It's perfectly possible to change SMD parts, although it's a lot easier with the right tools: solder tweezers or hot air gun. The cheap alternative is to put a big chisel bit on, heat the whole resistor and flick it off \$\endgroup\$ – pjc50 Jul 13 '16 at 18:25

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