万用表（此处我们用它测量电压，测量的目的电压为2.75-4.2/4.3V）
直尺（10cm-20cm均可）
光线明亮的环境
通常情况下18650电池的容量不会超过3100mAh(极限为3400mAh，任何超过的都是假货次货，均有爆炸危险哦。笔者在买高光手电同时配的电池是5000mAh的，对没错，小伙伴们惊呆了吧？ 很明显是虚标的)。 这里说一下专业词汇，定容：就是指确定电池容量。学过初中物理的小伙伴们都知道，电池内部也是有电阻的，当外部有负载形成闭合回路时，内部电阻也是要消耗电能的。 18650锂离子电池定容标准是0.5C. 那么什么是0.5C呢？这里的C值是指放电比率，它和放电时间互为倒数。举例解释一下，拿一个3000mAh的18650来说，如果放到用手电筒上持续使用了7小时，那么就是1/6=0.14C, 那0.5C放点呢？0.5C放电就意味着要在x小时内将3000mAh电量放完，1/x=0.5，那x=2，也就是2小时内放出3000mAh电量。由于W=UI,所以粗略算下就是3Ah/2h*3.7V=5.55W,也就是要放上5.55瓦的灯头（cree Q3 是3W的，Cree R2 是5W的）。 一般情况下，A品电芯被用作了电动车电池和电动工具电池，B品被卖给移动电源厂家做成移动电源。C品会被手电筒厂家买走，或者国内的小商贩收走。所以现在你知道那些标称4000mAh和5000mAh的18650电池是怎么回事了。Normally the 18650 lithium ion battery's capacity won't exceed 3100mAh for any reason(based the 0.5C capacity-testing standard). If you got a xxFire 18650 battery, and labeled 5000mAh or so, PLEASE DON'T RISK YOUR LIFE TO USE IT. It's always been this case. A grade 18650 cells for e-bikes and power tools. B grade for small assembly company of power bank product. C grade and those below C grade for flashlight uses.
18650电池出厂定价是以每1000mAh计算的。出厂价每1000mAh价格为3.6/4.0/6.0元,市面上的售价为8元左右的18650，抛去商家利润，再抛去批发商利润，单颗电池普遍在3.2左右，实际容量在800mAh左右。Some company will use LOW PRICE WITH HUGE CAPACITY to attract customers or even distributors. The price always be something around a 0.65 USD to 1.3 USD for one single 18650 lithium ion batteries. Now you dare to use it? No company will sell goods with a price which is much more lower than the cost. Besides now the labor cost is increasing in China. If there is, it could be
18650锂离子电池放电有截止电压，即电压低于2.75V时则需要停止放电，否则对电池造成伤害，影响寿命。所以手电筒里面的18650大多有保护板对其进行放电保护。
拿万用表测量放电完毕的18650电芯电压，如果两端开路电压（并非恢复电压）低于2.75V，那么说明电池厂家为了节省成本用了劣质的保护板。这里要说明一个专业术语:恢复电压，顾名思义，就是电池在进行完放电操作后，静置一定时间后测量得到的开路电压。
18650，这是一个锂离子电池标准型号，国际通行。18，指电池的直径为18mm，65指电池的高度/长度为65mm。Is it PCB protected?There's the risk to be deformed, leakage, explosion. Under the maniac price war, Some companies use low price PCB protection board or EVEN cut this part off. This kind of deeds make the market pay prices for the explosion-able 18650 batteries. It does not come easy to tell whether this a PCB inside. Here's a easy way but not very reliable way. The 18650 li-ion battery's dimension is 18mm by 65mm. 65mm is its length. A PCB protected 18650 would be at least 67-68mm. Yet the most reliable way is to buy it from a reliable seller.
拿支持测量18650电芯的长度。
手电筒内电池因为需要加装保护板，2-3mm厚，所以长度会在67.5-68mm左右。长度不够说明保护板未加装。
拿一支18650电芯，放在光线明亮处，观察其外观。
观察其喷码是否模糊、重影、喷码不清，电池金属位置是否磨损严重或者锈蚀，很多略知电池都是经过回收二手废电池通过重新注液，进行翻新的。在翻新过程中由于要进行开盖注液操作，而在开盖过程中，这样的电池在使用中极易发生危险。Is it reconditioned?For the original, it has a clear color and texture. Tidy and clean appearance. No scratch. It should be correctly labeled with Model No, Type, Capacity, Voltage, Negative and positive indications. Metal sheets no scratch, no blackened and greenished. If there's inconformity then you can tell it's not the original.