Hi
I am using some v small unbranded Lipo batteries with a capacity of 30mAH. Like these ones:

https://www.ebay.co.uk/itm/5-pcs-30...315864?hash=item28397efe98:g:oogAAOSwaeRZIkpA

I have been charging them with the generic cheap charging modules based around the TP4056 chip like this

https://www.ebay.co.uk/itm/Mini-USB...562474?hash=item233a92ebaa:g:4WMAAOSwo4pYP~6s

The vendors of the modules rarely mention the fact, but the the TP4056 is configurable by a resistor, depending on the battery capacity. I believe most of the ones sold have a 1.2k resistor which is suitable for a 1000mAH battery

TP4056 datasheet here:
https://dlnmh9ip6v2uc.cloudfront.net/datasheets/Prototyping/TP4056.pdf

It does not mention a battery capacity less than 130mAH.

Somewhat concerned, I measured the current going into the charger using a bench supply set to 5V, and a discharged battery (I don't know whether it is really discharged: it measures 0V - but I think it contains circuitry to cut off below 3V)

The current was initially about 200mA but within about 15 seconds it fell to about 50mA and 10 minutes later was down to 11mA and falling. About 2mA of this is accounted for by the charger itself. The initial current is high, but it doesn't last long, and 11mA or so seems about right. The battery doesn't get warm.

Should I be concerned about this from the point of view of a) safety and b) battery life, and replace the resistor?

 

http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

 

I rekon a 37K will set it for 35mA or as per datasheet 30K for 50mA.

 

The battery spec itself shows normal charge rate of 0.5C and max charge rate of 1C. So you really shouldn't be pushing more than 15 - 30 mA into that thing.

The data sheet is a bit confusing as to selecting that current limit resistor (and as you say the chart does not go below 130 mA), but I'd try 40k for R(iset).

 

The battery spec itself shows normal charge rate of 0.5C and max charge rate of 1C. So you really shouldn't be pushing more than 15 - 30 mA into that thing.

The data sheet is a bit confusing as to selecting that current limit resistor (and as you say the chart does not go below 130 mA), but I'd try 40k for R(iset).

This list goes to 50mA.

http://artofcircuits.com/product/tp4056-1a-micro-usb-li-ion-battery-charger-module-with-protection

 

Thanks - I hadn't actually seen those battery specs before, I just pasted one of many Ebay sample listings
About 3 hours later it's down to about 4mA, half of which is accounted for the module itself. The voltage is at 3.95V
The question really is - do those initial few seconds when it's well above 1C matter, given that it very quickly gets down to <1C?

 

Dd, you found more info than I did - all I had was the NanJing data sheet.

The battery the OP linked to appears to have some electronics built in. I didn't see any description of what was in there. May be just undervoltage cutoff or may be something more.

 

The question really is - do those initial few seconds when it's well above 1C matter, given that it very quickly gets down to <1C?

Could be creating a short-lived hot spot internal to the battery. Can't be good for it. I'd change the resistor (R(iset)).