AA Li-Ion battery charged with USB-C

mipix 7650 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.

Treść została przetłumaczona

Zobacz oryginalną wersję tematu

Report a violation of the law

Reply Cool? Ranking DIY | New topic

Notify about new articles

📢 Listen (AI):

#31 20962845 15 Feb 2024 14:44

mipix mipix

Level 38

Posts: 4067

Help: 495

Rate: 1475
» | Topic author Helpful post? (0)

Post #31
20962845 15 Feb 2024 14:44

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.
ADVERTISEMENT
#32 20971226 21 Feb 2024 00:29

Jacek Rutkowski Jacek Rutkowski

Level 28

Posts: 1330

Help: 69

Rate: 274
» | Helpful post? (0)

Post #32
20971226 21 Feb 2024 00:29

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...
Create an account, log in here. You will receive points by participating in discussions.
Join this discussion.

Install Elektroda application

Reply Cool? Ranking DIY | New topic

Notify about new articles

📢 Listen (AI):

Report a violation of the law

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.

FAQ

TL;DR: At 1.51 V output and about 140 mA current, these USB-C AA Li-ion cells act like tiny regulated power banks: “closer to a power bank than to an AA battery.” This FAQ helps buyers and tinkerers understand charging behavior, cutoff, real capacity, and safe device fit before replacing alkaline or NiMH cells. [#20913400]

Why it matters: A regulated 1.5 V Li-ion AA can solve low-voltage device issues, but its abrupt cutoff, limited output current, and USB charging quirks can also cause unexpected failures.

Option	Nominal output in use	Behavior near empty	Best fit from the thread
USB-C Li-ion AA	1.51 V regulated	Drops to 1.10 V, then 0 V	clocks, remotes, some mice, gas heaters
NiMH AA	about 1.2 V	gradual decline	general rechargeable use
Alkaline AA	about 1.5 V	gradual decline	simple low-drain devices
High-drain toys/motors	needs more current	may overload low-current USB-C AA	not confirmed suitable

Key insight: The main advantage is not raw capacity. It is stable 1.5 V output from a 3.7 V Li-ion cell, until the control chip forces a sharp low-battery transition and shutdown.

Quick Facts

The teardown found an LC9205D chip and a label stating 140 mA current capacity for the AA version; the measured output was 1.51 V with almost imperceptible ripple. [#20912923]
Measured discharge behavior was specific: 4.20 V to 3.15 V on the internal cell gives 1.51 V out, 3.14 V to 2.80 V gives 1.10 V out, and below 2.80 V the output becomes 0 V. [#20913806]
Charging status used three visible states in the thread: slow flashing = charging, solid LED = full with 5 V connected, and very fast flashing = cell fault/open circuit. [#20913400]
One later AliExpress sample cost PLN 13.50, took about one month to arrive, and accepted 670 mAh at 5 V, equal to 3.35 Wh input energy. [#20962456]

How does an AA Li-ion battery with USB-C charging keep a steady 1.5 V output, and what role does the LC9205D chip play inside it?

It uses a regulated converter, not the raw Li-ion cell voltage, to hold the output near 1.5 V. The teardown identified an LC9205D and measured 1.51 V at the terminals. "LC9205D is an integrated power-management chip that charges, discharges, and protects a 3.7 V Li-ion cell while feeding a regulated 1.5 V AA-style output." In the thread’s quoted description, one chip handles charging, discharging, and protection with only a few external parts. [#20912923]

What happens to the output voltage of a 1.5 V USB-C rechargeable AA cell as the internal Li-ion cell drops from 4.2 V to 2.8 V?

It stays near 1.51 V for most of the discharge, then drops sharply before cutoff. The measured ranges were 1.51 V output from 4.20 V down to 3.15 V on the internal cell, then 1.10 V from 3.14 V to 2.80 V, and finally 0 V below 2.80 V. That means the user sees a regulated plateau, a brief low-voltage stage, and then a shutdown. [#20913806]

Why does a USB-C rechargeable AA battery suddenly fall to about 1.1 V before shutting off instead of gradually weakening like an alkaline cell?

It falls suddenly because the converter regulates the output until the Li-ion cell reaches its protection threshold. An alkaline cell naturally sags over time, but this design holds 1.51 V until the internal cell reaches about 3.15 V, then the converter drops to 1.10 V and shuts off at 2.80 V. As the teardown author put it, it is “closer to a power bank than to an AA battery.” [#20913400]

How can I tell from the LED indicator whether a USB-C AA battery is charging normally, fully charged, or has a cell fault such as an open circuit?

You can read the LED by its blink pattern. Slow flashing means normal charging. A steady light means 100% charge, but only while 5 V is still connected through USB. Very fast flashing was observed on a failed unit and was interpreted as a cell fault caused by an open circuit. The packaging shown in the thread did not describe that fast-flash state. [#20913400]

What is LC9205D, and how is it different from a simple buck converter used with a separate charger and protection circuit?

LC9205D is a three-in-one battery-management and conversion chip, not just a simple step-down regulator. The thread’s quoted description says it combines charging, discharging, and protection for a 3.7 V to 1.5 V lithium “dry battery” in one IC. A plain buck converter would only reduce voltage. This chip also adds under-voltage, overcharge, short-circuit, overheating, and lithium-cell protection in the same device. [#20912923]

What is USB Power Delivery (USB PD), and why can branched USB-C charging cables be risky with rechargeable AA batteries or other 5 V devices?

USB PD is a USB charging standard that can negotiate voltages above 5 V, so a branched cable can create an overvoltage hazard if one branch triggers a higher profile. The thread warns that when one output connects to a fast-charging device, a voltage higher than 5 V may appear on all terminals. That can damage simple 5 V devices or rechargeable AA cells that expect only basic USB input. "USB Power Delivery is a charging protocol that negotiates voltage and current over USB-C, with higher-than-5 V operation as a key feature." [#20913962]

How does Qualcomm Quick Charge 2.0 differ from USB PD in the context of split charging cables and overvoltage risk?

Quick Charge 2.0 was described as less cable-aware, which increases concern with split cables. In the thread, one poster noted that older protocols such as Qualcomm Quick Charge 2.0 do not pay attention to cable type, unlike USB PD where negotiation and cable support matter more. The practical risk is the same: a branch intended for 5 V-only devices can see a higher voltage than expected. [#20914031]

Which devices are these 1.5 V Li-ion AA batteries actually suitable for, such as wall clocks, remotes, mice, and gas heaters, and which loads are too demanding?

They suit low-drain devices that benefit from a stable 1.5 V output. The thread explicitly mentions wall clocks, remote controls, and watches as good fits, and later users described successful use cases in an old mouse and a gas heater. Motorized toys were not tested, and the original teardown warned that overcurrent behavior was unknown. With a stated AA current capacity of 140 mA, demanding loads are the risky category. [#20912923]

AA Li-ion 1.5 V rechargeable batteries vs NiMH AA cells vs alkaline AA batteries — which is better for remote controls, clocks, and motorized toys?

For remotes and clocks, the 1.5 V Li-ion type is best when stable voltage matters more than simplicity. NiMH and alkaline cells decline more gradually, while the regulated Li-ion cell keeps 1.51 V for most of its run. The tradeoff is lower current on some versions, extra electronics, and abrupt cutoff. For motorized toys, the thread gives no positive test result, so alkaline or stronger rechargeables remain the safer choice. [#20912923]

How can I estimate the real capacity of a USB-C rechargeable 1.5 V AA battery from a measured 5 V charging input in mAh or Wh?

Convert the measured 5 V charge input to watt-hours first, then divide by 1.5 V for an optimistic equivalent mAh figure. In the thread, 670 mAh charged at 5 V gives 3.35 Wh. Dividing 3.35 Wh by 1.5 V yields about 2.23 Ah, or roughly 2233 mAh equivalent at 1.5 V before converter losses. That number is an estimate, not a true delivered capacity under load. [#20962456]

What is the right way to test the discharge capacity of a regulated 1.5 V Li-ion AA battery when a normal charger/tester does not recognize it?

Use an external load and time the discharge at the regulated output, not a standard charger/tester. 1. Connect a known resistor or device to the 1.5 V output. 2. Measure current and log runtime until shutdown. 3. Calculate delivered mAh or Wh from current, voltage, and time. One user suggested a 10 Ω, 0.5 W resistor for about 150 mA load, but the thread also warns that accurate measurement needs more than “a resistor and a clock.” [#20962845]

Why might a 9 V Li-ion replacement battery make a multimeter squeak, and what does that say about converter noise in these batteries?

The squeak points to switching-converter noise inside the regulated battery. One user reported that a multimeter worked normally on a regular 9 V battery or NiMH pack, but squeaked on a Chinese 9 V Li-ion replacement. He blamed the converter in the battery. That suggests some regulated replacement batteries inject audible or electrical noise, which can matter in sensitive instruments even when the nominal voltage is correct. [#20915496]

What practical problems come up when charging four USB-C AA batteries for a camera or blood pressure monitor, and what charging setups help?

The main problem is logistics, not chemistry. Four cells usually need four USB connections, so charging can become awkward unless you have several ports or a splitter cable. The thread notes that some sets include a 2-way branch cable, and multi-output USB-C splitter cables also exist. The risk is that a bad split setup can expose every branch to more than 5 V if fast charging activates, so simple parallel charging is not always safe. [#20913939]

How would a single 3 V regulated battery plus a dummy spacer compare with using two separate 1.5 V rechargeable AA cells in a remote control?

A single 3 V regulated battery plus a dummy spacer would simplify charging because you would charge only one cell. The proposal in the thread lists three benefits: conversion from 3.7 V to 3.0 V instead of 1.5 V, only one battery to charge, and possible charging with the cover removed instead of removing two cells. The drawback is that this was only a concept in the discussion, not a tested product. [#20917162]

Why do some AliExpress and Allegro listings for 1.5 V Li-ion AA cells claim very high capacities like 2600 mAh or 3300 mWh, and how should those numbers be interpreted?

Those numbers often mix different voltage bases, so they are easy to misread. A listing may quote mWh for the internal Li-ion energy or a 1.5 V-equivalent mAh figure after conversion. In the thread, buyers reported some cheap cells had about 700 mAh instead of the advertised 2600 mAh, and one 3300 mWh class listing drew skepticism. Treat such claims as marketing until you verify delivered energy at the actual 1.5 V output. [#20915496]