How can I replace 3 wire lipo battery with 2 wire or 6 wire battery

Thread Starter

soldra

Joined Aug 19, 2020
4
My tablet battery has swollen up so might spontaneously combust. It is 3.7v Lithium Polymer 2588158 with 4100mah and 3 wires. When I measure the charge current at the 5v usb port it is only 870mA so about 0.29C.


IMG_20180403_220123.jpg




I cannot find for sale a similar 3 wire battery that is thin enough to fit in the tablet. I can only find 2 wire or 6 wire batteries.
like this:

2 WIRE

https://www.amazon.com/4000mAh-2890...HDH4P/ref=psdc_10112773011_t3_B07MXV8C6Q?th=1

6 WIRE

https://www.amazon.co.uk/Trconelect...ords=asus+nexus+battery&qid=1597855373&sr=8-4

I presume the original battery relies on the tablet's own charging circuitry which monitors a thermistor in the battery via the third wire for safely charging.

Q.1 The 2 wire replacement battery has a small control circuit inside the battery but no thermisor wire for the tablet charging controller. Is it safe to charge a 2 wire battery without connecting a thermistor sensor to the tablet charging circuit? I mean to ask, do all 2 wire batteries internal control circuits prevent dangerous conditions when charing with just 2 wires? Does the 2 wire battery have an onboard thermistor which is monitored by it's internal control board instead of the tablet charging controller?

Q.2 How could I get the 6 wire battery to work?

(with the 2 wire battery I could trick the tablet charging controller to be always on by connecting the thermistor sensing wire to ground via fixed resistor. This will only be safe if the 2 wire battery is able to control the safe charging by itself hence my question). How are 2 wire batteries afe if they have no third wire?
 

Dodgydave

Joined Jun 22, 2012
9,666
The White wire is usually a Temperature sensor, this is connected to Negative terminal. You could replace it with a two wire one and use the thermistor from the old battery, .

Easily checked by using a DVM on Ohms and hold it in your hands to warm it up, it should change in resistance.
 

Thread Starter

soldra

Joined Aug 19, 2020
4
Thanks for reply.

I did think of that but how can I remove the thermistor without spontaeous combustion? Unlike the photo my battery has puffed up like a balloon.

I could buy a new thermistor from somewhere I guess and connect it. I did think of just connecting the thermistor wire to a fixed resistor and hope the 2 wire battery internal control board will take care of safety?

I have now ordered a 3 wire battery but it is only 2700mah compared with the original 4100mah.

The charging current with the original battery at the 5v USB port is 0.870A so I expect it is low enough not to overload the smaller battery.

Do you think the smaller battery will work OK? Are there any other considerations I might not know about e.g. I don't know number of cells, etc.
 
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