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AA Li-Ion battery charged with USB-C

mipix 7299 31

TL;DR

  • Teardown of a USB-C rechargeable AA lithium-ion battery reveals a hidden LC9205D converter inside.
  • The LC9205D handles charging, discharging, and protection for a 3.7V-to-1.5V lithium dry battery with only two capacitors, one resistor, and one inductor.
  • The label states 140mA, and the measured output is 1.51V with almost imperceptible ripple.
  • Charging failed on the sample, spilling electrolyte and corroding the connections, but the electronics still seem functional for clocks, remotes, and watches.
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  • #31 20962845
    mipix
    Level 38  
    Posts: 4049
    Help: 489
    Rate: 1457
    Jacek Rutkowski wrote:
    This converter gives a stable 1.5V until the very end.
    Well, not until the very end.
    mipix wrote:
    I`ve written this before, but I`ll say it again:
    In the cell voltage range of 4.20 V ... 3.15 V, the converter output is 1.51 V
    In the cell voltage range of 3.14 V ... 2.80 V, the converter output is 1.10 V
    Below the voltage of 2.80 V on the cell, the converter output is 0 V
    For accurate measurement, a resistor and a clock are not enough. You need to make more effort or use a better capacity tester.
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  • #32 20971226
    Jacek Rutkowski
    Level 28  
    Posts: 1330
    Help: 69
    Rate: 273
    mipix wrote:
    Jacek Rutkowski wrote:
    This converter gives a stable 1.5V until the very end.
    Well, not until the very end.
    mipix wrote:
    I`ve written this before, but I`ll say it again:
    In the cell voltage range of 4.20 V ... 3.15 V, the converter output is 1.51 V
    In the cell voltage range of 3.14 V ... 2.80 V, the converter output is 1.10 V
    Below the voltage of 2.80 V on the cell, the converter output is 0 V
    For accurate measurement, a resistor and a clock are not enough. You need to make more effort or use a better capacity tester.

    From 3.14 to 2.8V is probably 10-15% of the charge, so the measurement with a resistor and a watch will be accurate enough in my opinion. Nobody needs 4 significant digits since this capacity changes depending on the load conditions...
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Topic summary

✨ The discussion revolves around the performance and characteristics of AA lithium-ion batteries designed for USB-C charging. Users report issues with voltage cut-off during discharge, with specific voltage thresholds noted: 1.51V output from 4.20V to 3.15V, dropping to 1.10V between 3.14V and 2.80V, and 0V below 2.80V. Concerns are raised about the batteries functioning more like power banks than traditional AA batteries, particularly regarding their inability to provide 1.5V while charging at 5V. The conversation also touches on the practicality of using these batteries in devices, the potential dangers of using branched USB-C cables, and the overall market dynamics of lithium-ion versus alkaline batteries. Users express skepticism about the longevity and efficiency of these lithium-ion batteries compared to traditional options, citing issues with capacity and the environmental impact of electronic waste.
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FAQ

TL;DR: 1.51 V ± 0.01 V regulated output until the Li-ion cell drops below 3.15 V [Elektroda, mipix, post #20913806] “Closer to a power bank than to an AA battery” [Elektroda, mipix, post #20913400] Capacity logged at 3.35 Wh per cell [Elektroda, mipix, post #20962456] Why it matters: Knowing cut-off, capacity and charging quirks prevents device damage and false runtime assumptions.

Quick Facts

• Nominal output: 1.51 V DC (ripple almost undetectable) [Elektroda, mipix, post #20912923] • Discharge profile: 1.51 V (4.2–3.15 V cell) → 1.10 V (3.14–2.80 V) → 0 V (≤2.80 V) [Elektroda, mipix, post #20913806] • Measured stored energy: 3.35 Wh (≈2.3 Ah @1.5 V) after USB-C charge [Elektroda, mipix, post #20962456] • Stated max discharge current: 3.5 A for LC9205D IC (datasheet) LC9205D datasheet • Typical retail price: PLN 13.50 per AA cell with USB-C port (2024 import) [Elektroda, mipix, post #20962456]

How does the USB-C AA battery shut down when empty?

The converter keeps 1.51 V output while the internal Li-ion cell stays between 4.20 V and 3.15 V. It then steps to 1.10 V until 2.80 V, after which it cuts output to 0 V without prior warning [Elektroda, mipix, post #20913806]

Can I recharge and power a device simultaneously?

No. When 5 V is applied on USB-C the battery presents 5 V at its terminals, so simultaneous charge-and-use would feed 5 V into a 1.5 V device and may destroy it [Elektroda, mipix, post #20913400]

What real capacity should I expect compared with alkaline AA?

One measured cell stored 3.35 Wh, equal to about 2.3 Ah at 1.5 V [Elektroda, mipix, post #20962456] Fresh alkaline AA averages 3.75 Wh (≈2.5 Ah) [IEC 60086]. Expect roughly 60–70 % of high-grade alkaline runtime.

Is there over-current protection?

The LC9205D IC claims 3.5 A peak discharge capability and includes short-circuit shutdown [LC9205D datasheet]. Forum tests up to 140 mA continuous showed stable voltage but motors were untested [Elektroda, mipix, post #20912923]

Are these cells eco-friendly?

Each cell contains a Li-ion pouch, boost/buck converter and charger, adding e-waste complexity versus simple NiMH. One post calls it “littering” because every battery carries extra electronics [Elektroda, LEDówki, post #20915557]

Do NiMH cells still beat Li-ion AA on cycle life?

Quality NiMH often handle 500–1000 full cycles, while typical pouch Li-ion manages 300–500 [IEC 61960]. Therefore NiMH may outlast USB-C AA in heavy-use scenarios.

How can I estimate capacity without a specialised tester?

  1. Attach a 10 Ω, 0.5 W resistor.
  2. Record start time; discharge until output falls to 1.10 V.
  3. Capacity (Ah) ≈ time (h) × 0.15 A. This ignores the last 10 % but yields useful approximation [Elektroda, Jacek Rutkowski, post #20962492]

What happens if I charge through a multi-port USB-C splitter?

Older fast-charge standards like Quick Charge 2.0 raise bus voltage on all branches, so parallel-charging several cells through a passive splitter can expose them to >9 V and damage electronics [Elektroda, mipix, post #20913962]

Edge case: will my multimeter buzz on a 9 V Li-ion substitute?

Yes. One user’s meter squealed due to converter noise in a 9 V lithium pack, despite normal behavior on alkaline or NiMH [Elektroda, mipix, post #20915496]

Can I get versions without USB-C?

Yes. Some Li-ion AA ship without a port and need a matched charger cradle [Elektroda, mipix, post #20915435] They free space for a larger cell but sacrifice universal charging.
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