Stable 0.45 A Drain After Wake on a Redmi Note 11
A technician at a Bhubaneswar service centre receives a Redmi Note 11 that powers on but drops from 80% to 20% in about four hours with the screen off. The customer says the battery was replaced two months ago at a local shop. A USB power meter shows 0.02 A at idle after boot, but when the technician wakes the phone the draw jumps to 0.45 A and stays there with the screen locked and Wi-Fi off. The battery reads 3.82 V at room temperature, and the back panel feels slightly warm near the camera module. Charging is normal at 1.8 A. The technician has a thermal camera, a multimeter, a known-good battery and 90 minutes before the customer returns. The phone has no water-damage indicator triggered and no visible corrosion. She has not yet opened the shield can. The customer insists the phone worked normally before the battery replacement.
1. Using the current-draw readings, explain which subsystem is most likely responsible and why a second battery replacement is not the first step.
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At 3.82 V, 0.45 A is about 1.72 W. A 5,000 mAh battery stores roughly 19 Wh, so a 60% drop in four hours is about 2.85 W average. The 0.45 A reading alone does not account for the whole drain, but a stable 0.45 A with the screen locked is abnormal: a healthy phone should fall to tens of milliamps once it sleeps. The current rises only after wake and never falls back, which points to a subsystem or power rail being enabled and not returning to sleep. A failing battery more often shows voltage sag under load, early charging cut-off or swelling; here charging is normal at 1.8 A and the pack is recent. Replacing the battery again would be guesswork. The warmth near the camera module makes the camera, its regulator or a nearby PMIC rail the first suspects. The correct next move is to repeat the test with a known-good battery, then isolate subsystems before replacing any IC.
2. Outline a measurement sequence to localise the fault before any IC is replaced.
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- Reboot with a known-good battery, wait five minutes and record current with the screen off; compare with the original pack. 2. Boot into safe mode and then airplane mode to exclude third-party apps and radios. 3. Use the thermal camera before and after wake to find the hot area rather than guessing. 4. Disconnect the camera module and retest; if current falls, test the camera and its rail. 5. With the battery removed, use diode mode to check PMIC output rails for shorts, comparing with a known-good board. 6. Inspect the shield can, connectors and nearby passives for corrosion or cold joints. 7. Only after a rail is confirmed faulty should the charging IC or PMIC be replaced. Record each reading so the repair is evidence-based, not trial-and-error.
3. Write a short explanation for the customer covering why the previous battery may still be good and what the new repair involves.
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Explain in plain language: 'The battery is charging normally and holds voltage, so the problem is probably a part on the main board that keeps drawing power after the screen goes off. Replacing the battery again would not fix that.' State the plan: test with a known-good battery, use a thermal camera to locate the warm area, then isolate the faulty component. Give a realistic time and price range, and say that opening the board carries some risk. Avoid blaming the previous shop. Ask for approval before any board-level work and provide a written receipt with the fault, work done and warranty terms.