I have just broken my nexus 7 and I was about to salvage the battery. I was thinking of using it maybe to power my raspi or arduino.

My main question is how do I charge it?

I was thinking of cutting the connector from a mobile charger and putting the plus on the plus and the negative on the negative. Is this too simplistic?

Here is a photo of a nexus 7 battery. I am not sure why it has two reds and two blacks and some other coloured wires to make it even more scary :)

enter image description here


closed as off-topic by Chetan Bhargava, placeholder, Keelan, pjc50, Daniel Grillo Sep 16 '14 at 11:32

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  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – Chetan Bhargava, placeholder, Keelan, pjc50, Daniel Grillo
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  • \$\begingroup\$ Similar: electronics.stackexchange.com/q/118207/2028 \$\endgroup\$ – JYelton Sep 16 '14 at 3:05
  • \$\begingroup\$ Don't do that! You'll make the LiOn battery very mad and you don't want to be around when that happens! Seriously, the phone contains the actual charging circuitry and without it, you'll at best not charge the battery and at worse cause an explosion or fire! \$\endgroup\$ – DoxyLover Sep 16 '14 at 4:25
  • \$\begingroup\$ I thought as i was talking about circuits it was on topic, especially it might be useful in a more general sense as it would apply potentially to lots of mobile batteries. \$\endgroup\$ – Roger Hills Sep 17 '14 at 4:10
  • \$\begingroup\$ @DoxyLover You aren't an electronic engineer, don't you? \$\endgroup\$ – peterh Sep 17 '14 at 12:05

It may be a little easier than suggested above. I agree 100% with them - do not just add power or you will likely be sorry!

From your picture above, it is a little fuzzy, but it looks like the battery says it is a 3.7 nominal 4.2 volt max battery which means it is ONE cell. So all of the worries about balancing etc don't play here as there are no series cells to balance.

Why the extra wires? Usually they are to monitor for temprature, discharge rate, overdisharge protection etc.

There are a lot of $5-$10.00 CC/CV power sources on e-bay that you could hook up to the positive and negative poles to charge that battery. Set the CV to 4.2 volts and CC to something small to start to be safe and increase it if it takes too long to charge.

Using a simple multimeter you can determine for certain which are the positive and negative nodes of the battery.

OF Course, ignore all of this if your aove picture is wrong and the battery contains multiple cells in series!!

Be careful!


You would need a balance charger that is rated to charge that battery. If you just try and charge it, all what would potentially happen, is that it would charge one cell quicker than another. This can cause failure or rupture/explosion, since the output of both cells are connected. Which would be the red and black wires on the far ends of the plug, the four in the middle is for charging with a balance charger which you can buy at most hobby shops.


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