上周一个朋友跟我抱怨，说新买的无线充电器是个废物：手机放上去一晚上才充了六成，背面烫得能焐手。我让他把手机壳摘了再试——第二天他来道歉了，裸机半小时充进去 20% 多，温度也正常。元凶不是充电器，是他那个带金属装饰环的「轻奢皮革壳」。这种案例我这几年见得太多了，所以干脆把公开实测数据整理一遍，聊聊手机壳这个最容易被忽略的变量。

Last week a friend complained that his new wireless charger was useless: the phone gained barely sixty percent overnight and the back was hot to the touch. I told him to take the case off and try again — the next day he apologized. Without the case, the phone charged over 20% in half an hour at normal temperature. The culprit was not the charger, but his leather case with a decorative metal ring. I have seen this so many times that I decided to put the public test data together and talk about the most overlooked variable in wireless charging: the phone case.

先说材质，这是最硬的一条线。有实验室做过对比：0.5mm 的 TPU 软壳，充电效率只掉 5%–10%，基本无感；而 0.2mm 的金属壳，效率直接砍掉 40%–60%——注意，金属壳更薄，但更致命，因为金属会反射和吸收交变磁场，等于在发射线圈和接收线圈之间立了一堵墙。带金属装饰环、磁吸卡包这类「局部金属」的壳介于两者之间，效率掉 15%–30%，而且经常出现充电时断时续、手机反复响起连接提示音的情况。所以第一条避坑原则很简单：纯硅胶、纯 TPU、纯 PC 随便用，任何带金属件的壳都要打问号。

Material is the hardest rule. Lab comparisons show that a 0.5mm TPU case only costs you 5%–10% of charging efficiency — barely noticeable. A 0.2mm metal case, however, cuts efficiency by 40%–60%. Note that the metal case is thinner yet far more damaging, because metal reflects and absorbs the alternating magnetic field, effectively building a wall between the transmitter and receiver coils. Cases with partial metal — decorative rings, magnetic card holders — sit in between, losing 15%–30% and often causing the connection to drop and reconnect repeatedly. So rule one is simple: pure silicone, TPU or PC cases are fine; anything with metal parts deserves a question mark.

再说厚度。今年有媒体拿一款三合一无线充电器配六款不同厚度的壳做过一轮很细的实测，结论值得抄下来：0.3mm 的超薄 TPU 壳能稳定跑满 15W，磁吸定位不到两秒；1.2mm 的 PC 硬壳大多还能满功率，但已经开始出现小毛病——有的降到 13.6W，有的长时间充电会有轻微嗡鸣；到了 2.8mm 以上的厚重防摔壳，全军覆没：有的降到 7.5W 还过热，有的只剩 5W，还有双层结构的壳直接让手机镜头防抖报错。1.2mm，基本就是磁吸无线充的舒适区红线。

Then there is thickness. This year a reviewer ran a detailed test pairing one 3-in-1 wireless charging stand with six cases of different thicknesses, and the conclusions are worth writing down. A 0.3mm ultra-thin TPU case held a full 15W with magnetic alignment locking in under two seconds. At 1.2mm, hard PC cases mostly kept full power but small issues appeared — one dropped to 13.6W, another produced a faint hum during long sessions. Above 2.8mm, every rugged case failed: one fell to 7.5W and overheated, another managed only 5W, and a dual-layer case even triggered camera OIS errors. Roughly speaking, 1.2mm is the comfort-zone red line for magnetic wireless charging.

磁吸壳还有个更隐蔽的坑：吸得住不等于对得准。有博主实测过，非认证的磁吸壳虽然「啪」一声吸上去很爽，但磁环位置差个一两毫米，功率就能从 15W 掉到 7.5W——你还看不出任何异常，手机显示在充电，只是慢了一倍。这也是为什么我一直建议，用磁吸无线充或者磁吸无线充电宝的人，壳尽量认准带 MFM 认证的，贵个几十块，换来的是磁环位置和磁力强度都按标准来。夹在中间省钱，最后省掉的是充电速度。

Magnetic cases hide a sneakier trap: snapping on firmly does not mean aligning accurately. Reviewers have measured that an uncertified magnetic case can feel perfectly satisfying when it clicks into place, yet a ring offset of just one or two millimeters drops power from 15W to 7.5W — with no visible symptom at all. The phone still says charging, just twice as slow. That is why I keep telling people who use magnetic chargers or magnetic power banks to stick with MFM-certified cases. The extra cost buys you a magnet ring positioned and rated to spec. Saving money in the middle layer usually means losing charging speed.

最后给一套很实用的自查方法。第一招是「摘壳对照法」：怀疑充电慢，摘壳充十分钟、戴壳充十分钟，各记一次电量涨幅，差距超过三分之一，壳就是主要嫌疑人。第二招看发热：戴壳充电时背面明显比裸机烫，说明能量在壳那一层变成了热，长期这样对电池寿命没好处，尤其是整夜充电的人。第三招留意场景：现在很多家居公共场所无线充是嵌在桌板下面的，隔着桌板再隔一层厚壳，距离早就超出 Qi 协议的有效范围，充不进是正常的，别急着投诉咖啡馆。

Finally, a practical self-check routine. First, the case-off comparison: charge ten minutes with the case and ten minutes without, note the percentage gained each time — if the gap exceeds one third, the case is your prime suspect. Second, watch the heat: if the back feels clearly hotter with the case on, energy is being turned into heat inside that layer, which is bad news for battery longevity, especially for overnight chargers. Third, mind the scenario: many under-desk wireless chargers in cafes and hotels transmit through the tabletop already, and adding a thick case pushes the distance beyond the effective range of the Qi protocol — failing to charge there is physics, not a reason to complain to the barista.

顺带说一句选购视角的建议。真正靠谱的无线充电器厂商，尤其是做设计与定制、生产与销售一体的那类，规格书里会老老实实写一行「兼容壳厚 ≤ 3mm」或者「建议壳厚 ≤ 1.2mm（磁吸）」。这行小字比宣传页上的大字重要得多——它意味着厂商真的按带壳场景做过线圈功率和温控标定。下次挑多设备无线充或者充电底座，不妨先翻规格书找这一行，找不到的，直接下一个。

One last tip from a buyer's perspective. Serious wireless charger makers — especially those handling design, customization, manufacturing and sales in-house — will honestly print a line like "case compatibility ≤ 3mm" or "recommended case thickness ≤ 1.2mm (magnetic)" in the spec sheet. That small line matters far more than the big claims on the marketing page, because it means the coils and thermal limits were actually calibrated for real-world, case-on use. Next time you shop for a multi-device wireless charger, look for that line first. If it is missing, move on to the next product.

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