The short answer
Alignment and heat explain nearly all of it. The coils must line up within a few millimetres, and the phone deliberately slows or stops charging when it gets warm. Take the case off, remove anything metal including cards and magnets, and use the charger’s own power adapter rather than a random one.
Wireless charging transfers power through two coils, and the efficiency depends heavily on how well those coils align and how much material sits between them. Around 20 to 30 percent of the energy becomes heat rather than charge, which is why a wireless charger runs warm and why phones throttle it.
Cause 1: alignment
On a flat pad without magnets, the coils must overlap closely. A phone placed slightly off centre may still charge, and it will charge slowly and generate more heat. Small differences matter, especially on phones where the coil is not centred in the body.
Practical approach: place the phone, wait for the charging indicator, then move it a few millimetres at a time and watch the estimated time or the charging rate if your phone reports it. Once you find the position, note where the phone edges sit relative to the pad. Magnetic chargers solve this problem entirely, which is their main advantage.
Cause 2: the case
- Thickness. Most chargers work through about 3mm. Rugged cases exceed that.
- Metal. Any metal plate, including the ones for magnetic car mounts, blocks charging and can heat up dangerously.
- Cards and cash in a wallet case sit exactly between the coils. Bank cards can be damaged by the field, and they will stop charging from working.
- PopSockets and rings either block the coil or hold the phone at an angle.
- Magnets in a non-certified case can interfere with alignment detection on magnetic systems.
Test by charging with the case off. If speed doubles, the case is your answer, and a thinner or charging-compatible case fixes it.
If a metal object such as a coin, key or card gets between the phone and the charger, it can heat up significantly through induction. Keep the charging surface clear, and if you find something metal on a charger that is warm, be careful picking it up.
Cause 3: heat
Phones limit charging speed as they warm, and wireless charging generates heat by design. Symptoms are charging that starts fast and slows after ten minutes, or stops entirely and resumes later.
What helps:
- Charge in a cool place, not in direct sun or next to a radiator.
- Take the case off, since it insulates exactly where the heat is generated.
- Use a charger with a fan if you need fast wireless charging reliably, which is common on higher-wattage stands.
- Do not use the phone heavily while wirelessly charging, because the processor’s heat compounds the coil’s heat.
- Use a stand rather than a flat pad, which allows air to circulate on both sides.
Cause 4: the power supply
This is the most overlooked cause. A wireless charger rated at 15W needs an adapter that can supply well over 15W, because of conversion losses. Plugging it into an old 5W phone charger, a laptop USB port or a car socket that supplies little current produces very slow charging that looks like a charger fault.
Use the adapter supplied with the charger, or one rated at or above the wattage stated in its instructions, with the right protocol. Many fast wireless chargers require a specific fast-charge standard on the input side and fall back to slow charging without it.
Cables matter too. A thin or long cable causes voltage drop. Use the one supplied, or a short, properly rated one.
Cause 5: the phone’s own settings
- Optimised charging holds at 80 percent overnight by design. That is not a fault, and it explains a phone that sits at 80 for hours.
- Charge limits set to 80 or 85 percent do the same thing permanently.
- Battery saver modes on some phones reduce charging speed.
- Software updates occasionally change charging behaviour. If speed dropped suddenly with no other change, check whether an update coincided.
Wireless charging is fundamentally slower and less efficient than a cable. If you need a fast top-up before going out, use a cable. Wireless is for convenience over hours, typically overnight or at a desk, and expecting cable speeds from it will always disappoint.
Cause 6: the charger itself
Cheap chargers vary enormously. Signs of a poor one include a coil that is small or badly positioned, no certification marking, a fixed low output regardless of the phone, and excessive heat from the pad itself. Certified chargers are tested for the negotiation that lets the phone request higher power, and uncertified ones frequently fall back to the slowest mode.
If the same phone charges quickly on a friend’s charger and slowly on yours, and alignment and power supply are both correct, the charger is the variable.
Why does wireless charging stop overnight?
Usually optimised charging holding at 80 percent, or the phone pausing because it got warm. Both are intentional and protective rather than faults.
Is wireless charging bad for the battery?
The heat it generates is mildly harder on the battery than slow cable charging. Charging in a cool place without a case largely removes the difference, and normal use is not a concern.
Can I charge through a case?
Through most thin cases, yes. Through thick rugged cases, metal plates, wallet cases with cards or anything over about 3mm, often not. Test with the case off to find out.
Why is my wireless charging so much slower than the cable?
Because of conversion losses in both coils and the heat limits that follow. Wireless charging is typically half the speed of a cable at best, and that is normal rather than a defect.
Do magnetic chargers charge faster?
They charge more consistently, because perfect alignment means less wasted energy and less heat. On phones that support higher magnetic charging speeds, they are also faster outright.
The quick checklist
Case off, nothing metal between phone and pad, phone centred on the coil. Use the charger’s own adapter and a short cable. Charge somewhere cool, preferably on a stand rather than flat. Accept that 80 percent overnight is optimised charging working as intended. If it is still slow after all that, compare against another charger, because cheap pads frequently never negotiate past their slowest mode.
