"There is still charge in the power bank, but my phone stopped charging halfway — is it broken?"

"It has been plugged in for ages and the battery is stuck at 75% or 80%."

Before you blame the power bank: this is almost always your phone protecting its battery, and it is working as intended.

Phones have built-in battery health management

Modern smartphones — iPhone, Samsung, Pixel — nearly all switch to slow charging once the battery reaches roughly 70–80%. This is trickle charging.

In plain terms, the phone sips power in the final stretch so the cell does not get too warm, which extends its life. The power bank is still delivering steadily; the phone just is not in a hurry to take it.

Why does it sometimes slow at 75%, or stall at 60%?

Where the slowdown kicks in depends on conditions:

  • Ambient temperature is high — using the phone while charging in summer, or leaving it in a hot car, makes it throttle earlier to protect the battery
  • Fast-charging protocols do not fully match — if the charger and phone do not line up on PD, QC or PPS, the phone drops to a lower power level
  • Battery protection features are on — Apple's Optimised Battery Charging and Samsung's Protect Battery both deliberately cap charging speed to prolong battery life

Illustration of the three common reasons charging slows down: high ambient temperature, mismatched fast-charging protocols, and battery protection settings

Battery health affects charging speed too

This is especially visible on iPhones. As battery health declines, the slowdown starts earlier. Below roughly 80% health, the phone may begin easing off at 60–70%, and in extreme cases the percentage appears to stop climbing altogether.

Guidance that a battery below 80% health should be replaced, and that charging while using the phone in hot conditions should be avoided

If battery health is under 80%, replace the battery. And avoid using the phone while it charges, particularly somewhere warm.

In short: a power bank that seems to stop halfway is usually not faulty. The phone is looking after itself.

Power banks worth a look

Further reading