FAQ
TL;DR: If an HTC One M8’s battery is below about 3.4 V, a standard charger won’t revive it; “you have to unscrew the phone and measure the voltage.” [Elektroda, KRY5PIN, post #16662080]
Why it matters: This FAQ helps owners fix an M8 that shows an orange LED while refusing to boot.
Quick Facts
- Deep-discharge threshold: Approx. 3.4 V; standard charging won’t start below this level. [Elektroda, KRY5PIN, post #16662080]
- Precharge behavior: LED may blink until ~3.65 V, then normal charging begins. [Elektroda, OlekMTG, post #16736302]
- Charger capability: Use ≥1.5 A; 1 A may fail to initiate charging on a low battery. [Elektroda, OlekMTG, post #16736302]
- Bypass charging IC only to “excite” a dead cell with higher current; this requires skill. [Elektroda, FIsiu_, post #16662257]
- Hardware risk: Overheating and memory corruption are known; a new motherboard can be necessary. [Elektroda, mahamalak, post #16736853]
Why does my HTC One M8 show an orange LED but won’t turn on?
Two common causes are a deeply discharged battery or storage/bootloader faults. With heavy discharge, the LED may blink until voltage rises, then charging starts. Insufficient charger current (≈1 A) can prevent recovery. A constantly lit LED can also point to bootloader or NAND issues. Try a ≥1.5 A charger first, then test battery voltage. [Elektroda, OlekMTG, post #16736302]
What battery voltage is needed for the M8 to start charging normally?
If the cell sits below about 3.4 V, the phone’s standard charging won’t engage. Bring the voltage above that threshold before expecting normal behavior. The first step is to open the phone and measure across the battery terminals to confirm the voltage. “If it is below 3.4 V, you will not charge it with a standard charger.” [Elektroda, KRY5PIN, post #16662080]
Can I charge the M8 battery without opening the phone?
No. To recover a deeply discharged pack, you would have to bypass the internal charging circuit and apply a higher current directly. This procedure carries safety risks and should be done only by experienced technicians with proper tools and supervision. [Elektroda, FIsiu_, post #16662257]
How do I check the battery voltage safely?
Use a multimeter on DC volts and measure directly at the battery terminals after opening the device.
- Disconnect power and access the battery.
- Place the meter probes on the battery’s positive and negative terminals.
- Read the voltage; record it before further steps. [Elektroda, KRY5PIN, post #16735013]
My multimeter shows 0 V, but the LED lights—what’s wrong?
Recheck probe placement on the correct battery pins and ensure a reliable contact. A lit LED suggests some voltage is present, so a 0 V reading often indicates a measurement error. Use sharp probes, clean pads, and confirm meter range before concluding the battery is dead. [Elektroda, OlekMTG, post #16736302]
Is a 5 V/2 A charger enough to recover a low M8 battery?
Yes. A 2 A supply exceeds the minimum recommended current for initiating charging on a low battery. If recovery still fails with a solid 2 A charger and good cable, suspect the battery, charging circuit, or storage/bootloader faults instead of the adapter. [Elektroda, OlekMTG, post #16736302]
The phone warms up with a new battery but shows no display—what does that indicate?
Board heating without display often signals deeper hardware faults. On the M8, overheating and memory corruption are documented. In such cases, replacing the motherboard is a practical path when diagnostics confirm logic failure. Back up data expectations accordingly. [Elektroda, mahamalak, post #16736853]
Could a “new” replacement battery still be bad?
Yes. Users have received old or weak cells sold as new. One report noted an M8 that only lit the LED and drew almost no power until a properly functioning replacement battery was installed under warranty. Watch for low current draw despite normal indicators. [Elektroda, WLOTOP3237, post #17078641]
What does LED blinking versus steady mean during recovery?
When the M8 battery is very low, nothing may happen at first. Then the LED can begin blinking as the cell precharges. After reaching about 3.65 V, normal charging starts and behavior stabilizes. If the LED stays lit with no progress, look beyond the battery. [Elektroda, OlekMTG, post #16736302]
Which charger and cable should I use for best results?
Use a verified 5 V supply rated at least 1.5 A with a short, high‑quality cable. This helps the phone enter its recovery charge window if the battery is low. Under‑current adapters near 1 A may fail to trigger charging on a deeply discharged cell. [Elektroda, OlekMTG, post #16736302]
Is it worth repairing a refurbished or previously opened M8?
If seals are disturbed and non‑original parts are present, further investment often makes little sense. Prior unsuccessful repairs increase risk and cost. Consider parting out or replacing the device rather than chasing intermittent faults on a rebuilt unit. [Elektroda, OlekMTG, post #16738337]
Can I jump‑start a dead Li‑ion cell by bypassing the phone’s charger?
Technically, yes, but only with expertise. A technician can bypass the charging system and apply a higher current to re‑excite the cell. This involves fire and damage risk if done incorrectly. Do not attempt without proper tools, training, and safety controls. [Elektroda, FIsiu_, post #16662257]
What’s a quick diagnostic flow for an M8 that won’t boot?
Start with power integrity.
- Verify charger output (≥1.5 A) and cable.
- Measure battery; if <3.4 V, precharge first.
- If voltage is healthy (e.g., 4.0 V) yet no display, suspect logic faults. [Elektroda, KRY5PIN, post #16662080]
I measured 4.0 V on a spare battery but the phone still won’t display. What next?
A 4.0 V reading shows the cell is charged, so look beyond the battery. Inspect for overheating, storage corruption, or prior refurb damage. Motherboard replacement can be the most direct fix when the board warms and the screen stays black. [Elektroda, Mike20122, post #16738473]
What edge cases should I watch for when only the LED lights?
Watch for an aged or defective “new” battery that accepts charge yet delivers almost zero current. Another edge case is a lit LED from bootloader or NAND faults that block startup even with adequate voltage. Both require hardware-level diagnosis. [Elektroda, WLOTOP3237, post #17078641]
