The four independently monitored bays on the Golisi O4 auto-detect standard Li-ion, IMR, LiFePO4, NiMH, and NiCd chemistries, so the short answer is yes. Cylindrical cells in 18650, 20700, 21700, and 26650 formats drop in without spacers, and the bays run a CC CV charging method with overcharge, reverse polarity, and timer cutoffs on every slot.
This walkthrough covers the cell sizes that actually fit, how to pick the right current per bay, how to read the indicators, and the charging habits that keep cells healthy on a multi-bay unit.
What the Golisi O4 Is and Where Lithium-Ion Fits
The O4 is a four-bay smart charger built around four independent charging channels rather than a single shared circuit. Each bay runs its own detection logic and supplies its own adjustable current, so filling one bay or all four does not split available current across the slots. USB-C power input on current revisions, or Micro-USB on earlier runs, feeds the internal rails, and four spring-loaded bays handle the cell formats.
Lithium-ion sits inside the chemistry list the firmware recognizes, alongside LiFePO4, IMR, NiMH, and NiCd. Once a cell is inserted, the charger reads resting voltage and impedance, identifies the chemistry, and selects the matching charge profile with no button presses required. IMR (a manganese-stabilized Li-ion blend), standard Li-ion (ICR, INR), and lithium iron phosphate (LiFePO4 at 3.2 V nominal) all fall under that supported umbrella.
Physical Cell Sizes That Drop Straight In
Cylindrical formats from 18650, 20700, and 21700 through 26650 fit the spring-loaded bays without spacers. Smaller 18350 and 14500 cells sit lower in the same slot once the negative slider is pushed inward. The bay accepts any cell up to roughly 70 mm long, which covers most protected 18650s and many protected 21700s with a small PCB on the negative end.
What the O4 Does Not Do
The unit functions as a charger only and cannot discharge cells, analyze internal resistance, or act as a power bank. There is no USB-out port, so installed cells cannot top up a phone or another USB device. For a discharge curve or capacity-grading test, a dedicated analyzer is the right tool.
| Feature | Capability |
|---|---|
| Bays | 4 independent channels |
| Supported chemistries | Li-ion, IMR, LiFePO4, NiMH, NiCd |
| Supported sizes | 10440, 14500, 18350, 18650, 20700, 21700, 26650 |
| Charge currents | 0.5 A / 1 A / 2 A per slot |
| Power input | USB-C (current) or Micro-USB (older) |
| Display | Per-bay LCD: voltage, current, mAh, status |
| Safety features | Overcharge, short-circuit, reverse polarity, timer |
| Power-bank mode | Not supported |
Lithium-Ion Cell Sizes and Chemistry the O4 Accepts
Standard Li-ion and IMR cells in 18650, 20700, 21700, and 26650 fit the bays without spacers, and 18350 and 14500 sit lower in the same bay with the slider pushed inward. Because every slot accepts the same range, you can mix sizes across all four bays at once, charging a 26650 in bay one and a pair of 18350s in bays three and four in the same session.
Protected vs. Unprotected Cell Length
Protected cells up to about 70 mm clear the bay lid. Most name-brand protected 18650s measure around 65–68 mm, leaving a millimeter or two of headroom. Longer protected 21700s with extended PCM boards can push past 70 mm, so measuring before insertion is worth the thirty seconds. Unprotected cells, which usually run 65 mm for an 18650 and 70 mm for a 21700, fit with comfortable clearance.
Chemistry Auto-Detection and Exotic Formats
By reading resting voltage and impedance, the O4 eliminates the need to manually pick Li-ion for any standard cell you insert. A 3.7 V resting cell is read as Li-ion, a 3.2 V resting cell as LiFePO4, and a 1.2 V cell as NiMH without menu diving. Exotic formats such as LiPo pouches, 9 V rectangular blocks, or oversized 32650 cylindrical cells fall outside the O4’s design and should not be forced into the bays.
A pouch cell simply will not make contact, and a 32650 exceeds the spring travel.
| Cell Type | Length (Typical) | Fits O4 Bay? |
|---|---|---|
| 18650 unprotected | ~65 mm | Yes, with clearance |
| 18650 protected | ~65–68 mm | Yes, measure long-button cells first |
| 20700 / 21700 unprotected | ~70 mm | Yes, tight fit |
| 21700 protected | ~70–75 mm | Often too long, measure first |
| 26650 | ~68 mm | Yes |
| 18350 / 14500 | ~35 / 50 mm | Yes, with slider pushed in |
| LiPo pouch / 32650 / 9 V | Varies | No |
Tip: A quick check before insertion pays off. Hold the cell up to the open bay, eyeball the spring travel, and confirm the wrapper is intact. A cell that visibly bottoms out before contact is reached needs a spacer or a different charger.
Choosing the Right Current for Each Lithium-Ion Bay
The O4 offers 0.5 A, 1 A, and 2 A per slot, with most units defaulting to 0.5 A when only one bay is filled and stepping up only when the firmware confirms the input supply can support it. The current button on the side of the unit cycles through the three options, and the chosen rate shows on the LCD for that bay.
A single 2 A charge pulls more current than some USB ports deliver reliably, so the four-bay default of 0.5 A is the conservative baseline.
Matching Current to Cell Rating
High-drain 18650 and 21700 cells rated for 3 A or higher continuous discharge can usually accept 1 A or 2 A charging without thermal stress. A 3000 mAh 18650 rated at 10 A continuous, for instance, handles 1 A and 2 A charge rates comfortably because both sit well below the 2 A charge ceiling most datasheets list.
Older or lower-grade 18650s, or any cell not rated above 1 A charge current, should stay at 0.5 A to preserve cycle life.
Why Matching Current Matters
Pushing 2A into a 1.6Ah 18650 will shorten its cycle life, and the LCD readout lets you confirm the actual delivered current before that damage adds up. A 0.5 A charge on a 2500 mAh cell finishes in roughly six hours; 1 A finishes in about three; 2 A in roughly 90 minutes.
The trade-off is heat: a fast charge warms the cell, and warmth plus high state-of-charge is the worst combination for Li-ion cathode stress.
Keeping that heat stress in mind, the next decision is how much current to feed each bay during a real session.
| Charge Rate | Best Cell Match | Typical Finish (2500 mAh) |
|---|---|---|
| 0.5 A (default) | Any Li-ion, safest for older cells | ~6 hours |
| 1 A | Cells rated ≥ 1 A charge | ~3 hours |
| 2 A | High-drain cells rated ≥ 2 A charge, single-bay use | ~1.5 hours |
Tip: Slow charging at 0.5 A is the gentlest option for most cells, and the O4’s default behavior already starts there. Reserve 2 A for single-bay sessions on cells whose datasheet clearly lists a 2 A charge ceiling.
Step-by-Step First Charge With a Lithium-Ion Cell
A clean first charge takes about ten minutes of attention and sets the habit for every session after it. The inspection step at the front matters more than the order of operations that follows.
- Inspect the wrapper. Look over the cell for nicks, tears, exposed nickel, or dents. A torn wrapper near the positive vent is a retire-the-battery situation, not a wrap-and-go.
- Match the bay to the cell. Slide the negative contact inward for 18350 and 14500, leave it out for 18650 and up. Drop the cell positive-end up, matching the polarity marking inside the bay.
- Confirm centered seating. The cell should sit straight and flush against both contacts. A misaligned spring contact is the single most common cause of an LCD that never wakes.
- Plug into a known-good USB source. A 2 A-rated wall adapter or a powered USB hub delivers the current the O4 expects. Under-powered ports cause the unit to throttle or refuse to start.
- Watch the LCD wake. Each occupied bay should show a recognized voltage, chemistry icon, and current rate within a few seconds of insertion.
- Let it run uninterrupted. A full charge takes one to six hours depending on the current rate. Pulling cells mid-cycle to top them off later shortens cycle life.
- Remove at full charge. Once the status indicator marks the cell complete, lift it out within a reasonable window rather than parking it for hours.
Tip: A wrapper repair kit costs a few dollars and adds years to a cell. Any cell with exposed nickel or a torn top should be rewrapped or retired before it ever nears a bay.
Reading the O4’s Status Lights and Display
The LCD on the O4 does most of the talking, but the indicator LEDs add a faster at-a-glance signal for each bay. Reading them correctly avoids the “did it finish or did it error” confusion that sends people chasing good cells.
Charging, Full, and Error Indicators
A solid or steady-color light typically signals active charging, while a fully lit or green indicator marks a completed cell at roughly 4.2 V for standard Li-ion. A red, flashing, or strobing LED usually points to a bay error such as reversed polarity, poor contact, or an unreadable cell. LiFePO4 cells complete at 3.65 V instead of 4.2 V, so the full cutoff is chemistry-aware rather than a single voltage threshold.
What the LCD Numbers Tell You
The per-bay LCD shows real-time voltage, current, and accumulated capacity in mAh, which is useful for comparing cells and spotting weak ones. Two 18650s from the same batch should finish within about 50 mAh of each other; a 600 mAh gap on a 2500 mAh cell usually means one is aging out. The mAh counter resets when the cell is removed and the bay goes empty.
What to Do If the LED Flashes Red
Pull the cell and inspect the wrapper, polarity, and spring alignment before inserting another. If a second known-good cell still triggers a flashing red on the same bay, the bay itself is likely at fault. Stop using that bay and contact the seller or manufacturer rather than cycling more cells through it.
A single suspect bay is one thing, but leaving any charger running unattended for hours multiplies the stakes.
| Indicator State | Meaning |
|---|---|
| Solid red / charging icon | Active charge in progress |
| Solid green / full icon | Cell complete (~4.2 V Li-ion / ~3.65 V LiFePO4) |
| Flashing red | Bay error: reversed polarity, poor contact, or unreadable cell |
| LCD shows 0.00 V after insertion | Spring not contacting cell, cell upside-down, or dead cell |
| LCD wakes then shows “null” | Chemistry outside supported list, usually a damaged cell |
Warning: A flashing red that persists across multiple cells in the same bay points to a bay-level fault. Stop using that bay and reach out to the seller or manufacturer rather than chasing it with new cells.
Safety Habits and Overnight Charging on a Multi-Bay Unit
Multi-bay chargers are designed to finish a job and be cleared out, not to hold cells for hours past full charge. A few habits keep the O4, the cells, and the room safe.
Surface, Location, and Enclosure
A ceramic countertop in a ventilated room beats a wooden nightstand inside a closed drawer every time. A tile countertop, a metal tray, or a stone windowsill all work; a wooden nightstand or a fabric pouch does not. Ventilation matters because even a healthy Li-ion cell releases a small amount of heat during the constant-voltage phase of CC CV charging, and that heat needs somewhere to go.
Overnight Charging Trade-offs
Avoid leaving cells on the charger long after they hit full, since multi-bay units can sit at elevated voltage that stresses Li-ion chemistry overnight. The O4’s overcharge protection cuts the charge at the correct voltage, but a cell parked at 4.2 V for eight hours is still sitting at a high state-of-charge, which is harder on the cathode than a cell that drops to storage voltage within an hour of completion.
What to Do When Something Feels Off
If a bay ever flashes red or a cell feels warm after removal, stop using that cell and that bay until the issue is identified. A warm cell on completion is normal; a hot cell that you cannot comfortably hold is not. Store topped-up cells in a protective case at room temperature rather than back in the charger as a makeshift holder.
A silicone sleeve or a hard plastic case costs little and keeps the wrapper and terminals safe between sessions.
Warning: Never charge a cell that smells sweet, looks puffy, or has a vent scar. A swollen Li-ion is at the end of its safe life regardless of what the charger says. Dispose of it through a proper e-waste or battery-recycling channel.
Bottom Line
The Golisi O4 is a safe pick for the common Li-ion formats in your collection, and the built-in protections plus per-bay LCD make it hard to misuse once you know what the indicators mean. Match the charge current to the cell rating, default to 0.5 A for anything questionable, and clear the bays promptly at full charge.
The single best habit is the simplest: pull cells within an hour of the green light and store them in a case off the charger.
FAQ
Can the Golisi O4 charger safely charge lithium-ion batteries?
Yes. The O4 supports standard Li-ion, IMR, and LiFePO4 chemistries with auto-detection, applies a CC CV charging method, and includes overcharge, short-circuit, reverse polarity, and timer protections on every bay.
What battery chemistries does the Golisi O4 support?
Li-ion (ICR, INR), IMR, LiFePO4 (3.2 V nominal), NiMH, and NiCd. The unit reads resting voltage and impedance to pick the right charge profile without manual selection.
Is the Golisi O4 compatible with 18650 lithium-ion cells?
Yes, 18650 is the flagship supported size. Both protected (up to about 68 mm) and unprotected versions fit the bay with comfortable clearance, and the spring contact adjusts for 18350 and 14500 in the same slot.
Will the Golisi O4 charge 21700 or 20700 lithium-ion batteries?
Yes. Unprotected 20700 and 21700 cells fit the bay at roughly 70 mm, and protected versions up to about 70 mm clear the lid. Longer protected 21700s with extended PCM boards should be measured before insertion.
How do I know when a lithium-ion battery is fully charged on the Golisi O4?
The bay’s green LED and the LCD “full” icon mark a completed cell at roughly 4.2 V for standard Li-ion or 3.65 V for LiFePO4. The accumulated mAh reading stops climbing once the cell reaches that cutoff.
How long does it take the Golisi O4 to charge a lithium-ion battery?
Charge time depends on the current rate and cell capacity. A 2500 mAh 18650 takes roughly six hours at 0.5 A, three hours at 1 A, and about 90 minutes at 2 A.
