KNULLI Scarab Battery Percentage on RG CubeXX: BatteryPlus Calibration and Limits

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Scope and safety

This documentation-led guide applies only to Anbernic RG CubeXX running KNULLI Scarab 20260511, specifically the release image knulli-h700-rg-cubexx-scarab-20260511.img.gz. No owner hardware was tested, and no measured result is claimed.

The preferred endpoint is read-only: verify the device and release, open System Information, record the BatteryPlus wording actually displayed, and stop. A percentage is a software estimate—not a battery-health result or safety certificate.

If the device shows swelling, smoke, smell, unusual heat, visible damage, liquid exposure, or unstable charging, stop. Disconnect external power if it is safe to do so and seek qualified service.

Short Answer

BatteryPlus is a feature introduced in KNULLI Scarab. KNULLI describes it as a voltage-based battery-percentage system: it estimates percentage from measured voltage instead of relying on the percentage reported by the power-management integrated circuit (PMIC).

That distinction does not make BatteryPlus independently or laboratory accurate. Its calibration establishes a software value named V_FULL, which BatteryPlus uses as its 100% voltage anchor. KNULLI stores that calibration data on the SHARE/userdata partition.

The safest first check changes nothing:

  1. Verify RG CubeXX and Scarab 20260511.
  2. Press Start to open the main menu, then go to System → Information.
  3. Record the actual BatteryPlus calibration wording shown. Record the mode only if the screen shows it.
  4. Stop.

KNULLI does not document the exact field caption or value strings on that screen, and it does not promise that the active mode is displayed. Do not invent or normalize a label: copy what your own screen says.

Release Boundary: Scarab 20260511 Only

The Scarab release publishes the RG CubeXX image knulli-h700-rg-cubexx-scarab-20260511.img.gz, and its release notes introduce BatteryPlus. This article does not establish that a reader installed that image merely because an RG CubeXX is present; verify the release before following the procedure.

If you still need the correct release context, use the RG CubeXX Scarab installation and first-boot guide. That guide owns the installation workflow; it is not repeated here.

The evidence reviewed for this article does not establish BatteryPlus for RG CubeXX on Firefly 20241204 or Gladiator II 20250813. Do not apply Scarab’s BatteryPlus modes or calibration procedure to either release. Stock firmware, unknown builds, and custom or backported builds are also outside this procedure.

BatteryPlus Versus the PMIC Percentage

A PMIC can provide a hardware-reported percentage. BatteryPlus instead uses a voltage-based estimate. KNULLI gives a low-percentage example for the broader Anbernic H700 RG XX family, but that family-level example is not an RG CubeXX runtime promise, a minutes-remaining conversion, or a measured result from this article.

Some applications may bypass BatteryPlus and obtain their estimate directly from the PMIC. Two screens can therefore disagree without either screen proving battery health, usable capacity, or remaining runtime. The documentation does not provide an app-by-app list.

Read-Only Check: Record the Screen and Stop

  1. Confirm the handheld is an RG CubeXX from its casing, package, or manual. Do not infer the model from another H700-family device.
  2. Confirm it is running KNULLI Scarab 20260511. If the interface exposes an image or build identifier, record it exactly. If it shows Firefly, Gladiator II, stock firmware, an unknown build, or a custom/backported build, stop: this procedure does not apply.
  3. Press Start to open the main menu.
  4. Go to System → Information.
  5. Record only the wording the screen actually shows about BatteryPlus calibration. Record the active mode only if shown; the documentation does not promise that it will be.
  6. Record the verified model and release context, then stop.

Do not edit configuration, discharge the battery, time runtime, compare multiple applications, or infer capacity, health, or accuracy. If expected information is missing or worded differently, record a UI/documentation mismatch rather than guessing a label or diagnosing hardware.

Optional One-Time Calibration

Calibration is optional and secondary to the read-only check. It is not required maintenance, a repair, a health test, or a Retro Fix Lab owner test.

Before connecting power, read the existing RG CubeXX charging-specification and USB-C boundary guide. It owns the charger, cable, and charging-safety boundary; this article does not repeat or expand that advice.

  1. Keep the RG CubeXX powered on.
  2. Following KNULLI’s wording, plug it into a wall charger within the linked guide’s boundary.
  3. With the device still powered on, let the displayed percentage reach 100%.
  4. Disable auto suspend/shutdown if needed so the powered-on procedure can finish.
  5. Unplug the charger once.
  6. Wait about 15 seconds.
  7. Press Start to open the main menu, then return to System → Information.
  8. Record the calibration wording actually shown. Record the mode only if it appears.
  9. Stop.

Do not follow this with a discharge test, runtime test, deep discharge, or repeated charge cycle. Displayed 100% is an input to KNULLI’s software procedure, not proof of electrical full charge and not a safety certificate.

voltage and pmic Modes

KNULLI documents two BatteryPlus modes:

  • voltage — the default and recommended mode;
  • pmic — the fallback to the hardware-reported percentage.

Fallback does not mean universally more accurate. The read-only endpoint succeeds without changing modes.

If you deliberately choose to edit the optional setting, KNULLI places knulli.conf in the system folder of the userdata folder (often written as the shorthand userdata/system/knulli.conf). Back up and preserve the existing file rather than replacing it, then change only the applicable line in a plain-text editor:

system.batteryplus.mode=voltage

or:

system.batteryplus.mode=pmic

Use the KNULLI userdata backup guide before editing; file-transfer steps are outside this article. After a mode change, KNULLI says a reboot might be required so services listening for BatteryPlus updates restart.

Data Persistence and Environment Changes

KNULLI says BatteryPlus calibration data is stored on the SHARE/userdata partition. That makes calibration an environment-resident software state, not a permanent battery property.

When KNULLI detects a different device or environment in a multi-device or multi-storage setup, calibration can reset to defaults. Recheck Start (open the main menu) → System → Information rather than assuming the previous state persisted. This does not mean that TF2 always resets calibration, and the documentation does not enumerate every possible trigger.

For bounded storage context, see KNULLI microSD roles and formats. For protection of userdata-resident state before an update or card change, use the backup guide. Neither guide changes what calibration proves.

Some apps may bypass BatteryPlus and use PMIC estimation even when BatteryPlus is calibrated.

What Calibration Proves—and What It Does Not

Calibration establishes and stores BatteryPlus’s V_FULL 100% voltage anchor in the current SHARE/userdata environment.

It proves only that software-anchor state. It does not prove:

  • true electrochemical state of charge;
  • electrical full charge or correct charge termination;
  • usable battery capacity or battery health;
  • remaining minutes or workload-specific runtime;
  • accuracy of the voltage measurement or voltage-to-percentage curve;
  • charger, cable, USB-C, or PD suitability or compliance;
  • charging speed or charging behavior;
  • agreement in every application;
  • behavior on Firefly, Gladiator II, stock firmware, another H700 device, or a custom build.

An uncalibrated state is not a diagnosis of a faulty battery or handheld. A calibrated state is not a battery certificate. No owner observation, measured voltage, measured runtime, or charging result is presented here.

Excluded Systems and Tests

This procedure does not interpret physical charging/status indicators or RGB lighting, select charging accessories, test runtime or capacity, deliberately deep-discharge or repeatedly cycle the battery, or instruct enclosure opening, cell disconnection, electrical probing, or bench-supply use. Those systems and tests cannot be inferred from BatteryPlus calibration wording.

FAQ

Does “calibrated” mean the battery is healthy?

No. It means BatteryPlus has stored its V_FULL software anchor in that userdata environment. It does not measure battery health or usable capacity.

Does displayed 100% prove the battery is electrically full?

No. Displayed 100% is the software reading used in KNULLI’s optional procedure. It is not electrical validation or a safety certificate.

Is an uncalibrated result a hardware fault?

No. It is a software calibration state, not a battery or device diagnosis. Environment changes can reset calibration to defaults.

Why can another application show a different percentage?

Some applications may bypass BatteryPlus and use PMIC estimation. KNULLI does not provide a verified app list, and calibration does not guarantee cross-app agreement.

Should I change from voltage to pmic?

Not by default. KNULLI documents voltage as default/recommended and pmic as fallback. The read-only check and optional calibration do not require a mode edit.

Does this procedure apply to Firefly or Gladiator II?

No. The reviewed Firefly 20241204 and Gladiator II 20250813 release evidence does not establish Scarab BatteryPlus behavior for those builds.

Should I repeat the cycle until the percentage looks right?

No. KNULLI’s documented calibration is an optional one-time procedure. Stop after the single unplug, approximately 15-second wait, and System Information recheck.

Screenshot Guidance

If a correctly sourced screenshot is used, its caption should preserve the exact release scope: “RG CubeXX System Information on KNULLI Scarab 20260511; the screenshot documents only the wording displayed by this software environment.”

Crop to the relevant System Information area. Redact usernames, hostnames, IP/MAC addresses, account identifiers, serials, personal filesystem paths, network-share names, QR codes, notifications, and unrelated nearby-device or library details. Preserve only the release and BatteryPlus wording needed for context. A screenshot proves displayed wording only—not battery health, electrical state, percentage accuracy, or an owner-tested result.

Related Guides

Sources