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I recently salvaged this small (30 x 9.5 x 3.5 mm) LiPo single cell battery from an old device that lied broken for at least 3 years.

enter image description here

Therefore I expected it to be garbage ready for recycling, but when I measured its voltage it read 2.8V, so it seems to be in good shape. Hence I decided to keep it in my junk bin for experimentation purposes.

The problem is that I couldn't find any datasheet or info on the Internet, so estimating its capacity is a problem. In particular, I'm well aware of the LiPo charging technique that requires a constant-current phase followed by a constant-voltage phase, as this TI application notes explains. Excerpts:

At present, the major Li-Ion cell manufacturer recommends 4.200 +/- 50 mV as the ideal set point voltage, and 1c (a charging current rate equal to the A-hr rating of the cell) as the maximum charging current that can be used.

[...]

enter image description here

Since I never played a lot with LiPo batteries, I'm clueless at guessing its capacity (for what I know it could be anything between 100mAh and a couple of Ah).

Can anyone suggest me, if possible, a reasonable and safe estimate for its capacity or C rating, so that I won't be risking to overcharge it in the CC phase?

EDIT (to incorporate some more info, as prompted by comments)

  • the cell weighs approximately 1g (something between 1g and 2g)

  • it was embedded in an old (6-7 years) Bluetooth receiver for indoor usage (one of those small boxes that can be connected to the headphone jack of an amplifier to send the PC audio to your Hi-Fi system or whatever)

  • as far as can be seen by close visual examination, it doesn't embed any protection circuitry

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  • \$\begingroup\$ Weigh it. It'll be between 200 and 300 Wh/kg, probably on the low side for such a small cell. Divide by nominal voltage to get an Ah rating. Then charge at 0.5C to be on the safe side, at least the first time. \$\endgroup\$ – Brian Drummond Apr 2 '18 at 19:35
  • \$\begingroup\$ These are cheap cells with only about 150~300 mAh when used with a 10h Discharge but consult with Muni. About disposal. You might 1% if this now. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Apr 2 '18 at 19:45
  • \$\begingroup\$ @BrianDrummond Nice suggestion. Unluckily the highest resolution scale I've got has a 1g resolution (3kg full range). It reads something between 1g and 2g. I fear the measurement is affected by too much error. Anyway, using 1g as its value, 200Wh/kg and 3.6V nominal voltage, I get 55mAh. Sounds reasonable? \$\endgroup\$ – Lorenzo Donati -- Codidact.com Apr 2 '18 at 19:47
  • \$\begingroup\$ This is a kind of cells used in micro-helicopters-quadcopters. For this size the cell capacity is about 120 mAh \$\endgroup\$ – Ale..chenski Apr 2 '18 at 19:54
  • \$\begingroup\$ Good enough for a first charge. Or you could make a Ng weight from cardboard , cut it into N pieces, and cut one of those in 10 to increase resolution. \$\endgroup\$ – Brian Drummond Apr 2 '18 at 19:57

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