Why E-cigs get burning hot during recharging 

With the induction of new and stronger vaping devices, the e-cig lovers must understand the behavior of these devices for a safe and enjoyable experience. These devices are so powerful that they can generate enormous heat during the charging process. It is more relevant to devices with lithium ion batteries. They can actually get hot enough to even touch. However, there is nothing to be alarmed since the reason for this heating is very simple and you can easily handle that. 

What can be the reason of e-cig getting hot during charging?

1.Battery Chargers
It is always advisable to use the proper battery charger supplied with your e-cig. Improper battery chargers can overheat the vaping kit. Using the suitable battery charger for the charging operation also increases the life and reliability of the e-cig. 
You must consider a number of factors while selecting the most suitable changer for your vaping device. The most important is the size of battery that your device holds. It is usual for standard chargers to properly charge many types of batteries. However, certain types of batteries (21700 and 20700 etc.) cannot be properly charged by standard 18650 chargers. It is because, these batteries have much higher capacity than the charger’s capacity. Incidentally, these 20 series batteries are standard for modern vaping devices, hence older charger models cannot charge them properly.
Modern chargers are available loads of additional features like data bank, power bank, and blue tooth ability etc., apart from the regular charging feature. However, the features that affect its performance in safe and efficient battery charging are following: 
oReverse polarity feature that doesn’t allow a charger to operate if it is inserted in reverse pattern. 
oOver-charge protection feature stops charging as soon the batteries are fully charged to reduce battery stress.
oLi-ion composition, that is fast becoming the industry standard. 

You must always choose the best quality battery for your vaping device. It is common for a low-quality battery to overheat. This can even be the cause of a fire. For such reasons, a Li-Ion battery is the best all round choice since they designed to shut down charging upon overheating. This ensures safety and smoother device function.  
However, these modern batteries need ventilation. In case, MOD design doesn’t carry a ventilation mechanism, then you should opt for standard quality batteries. 

What you should keep in mind while looking for higher quality batteries?
oManufacturer or brand of the battery
Battery brand or the manufacturer is the most important factor when shopping for a 18650 battery. Basing on the price and quality, you cannot equate a lower priced battery with a top quality brand. Neither, you can trust the ratings and reviews. It is understandable for any battery manufacturer to look for selling as many batteries as possible. However, certain companies make exaggerated or false claims about their products to generate more sales. This is a very nasty and unlawful trend. Luckily, there is a standard ascertaining company called “Battery Smooch” that tests the batteries and verify the manufacturer claims. 
Five global brands; Sony, Samsung, LG, Sanyo, and Panasonic are renowned for supplying safe and trust worthy batteries. Batteries from these brands are worth buying owing to their brand name, stringent testing and strict quality control policy.  They are manufactured to provide even better performance than the specifications by the manufactures. 
oCapacity of a battery
The battery capacity rating indicates how much power it can supply for how many hours. It is mentioned in mAh (milliampere hours). It is a natural wish for anyone to enjoy the use of as powerful battery as one can get. However, capacity of a battery is restricted by its CDR (current rating). It is related to how much material can be stored inside a battery. A user has to make a choice between a higher current carrying battery and a higher capacity carrying battery. It is common for a high current battery to have a lower capacity. Typical examples of some of the famous batteries in the market are that Panasonic NCR18650B carry a very high capacity of 3400 mAh with just a minimal current rating of 4.9A.
Interestingly, there are some Samsung models of batteries that are designed to provide a nice balance of current and capacity. LG HG2, 25R, 30Q from Samsung as some of these batteries. 
oBattery performance factor called CDR (Continuous Discharge Rating)
The first thing you need to know is the volume of current your device needs for proper functioning. This is the most critical factor to understand in choosing a battery. Just in case, you chose an under powered battery, your device will overheat. Pulse (pulse discharge rating) and CDR (continuous discharge rating) are the two terms that are important to understand when we are talking about current rating of the batteries. 
Pulse (Pulse Rating) – it is the maximum rate of discharge of a battery that can be done for shorter time periods without life reduction or battery damage. 
Continuous Discharge Rate (CDR) – It is the maximum current rate which is safe for battery discharging over continuous period. Discharging a battery beyond these limits can cause serious battery degradation and even failure. 
Ratings related to pulse depend on a great number of factors like length of the pulse, rest time between two pulses and temperature of the battery. It for this complexity, that a battery is not usually evaluated on pulse factors. It is more common to employ CDR rating standards to rate a battery for quality and performance. 
oBattery Operation Temperatures  
Battery temperature is a critical factor in battery life. You need to maintain lower battery temperature to increase its life and efficiency. In all such cases, where a battery temperature consistently higher than 45 degrees, it is a clear sign that its charging is under powered. The danger of battery leakage or even bursting is high under such conditions, especially for Li-Ion batteries. To avoid such issues, Higher CDR rated batteries are definitely a better option.
oShould you select a Button Top or Flat top battery?  
Some devices are unfit or inserting button top batteries since they come with surface protuberance that doesn’t allow them to fit in the device body. In such cases, flat top batteries will work. They are shorter in size and they don’t obviously fit in the body of devices requiring longer batteries. These are vital factors in assessing whether you need flat top or button top batteries for your device. 

Some additional facts that must be in your knowledge:
oIt is always smarter to charge an internal battery with the specified charger. It is important to understand that a USB cable is only meant to connect your battery with the charger. No USB comes with a charger and you must always connect it with a charger carrying not more than an ampere and 5 volts capacity. You can damage your battery by charging it with an over powered charger. Your average USB Chargers in the car or chargers meant for cell phones have higher charging values. Similar is the case with USB connected to a computer. You must always chargers supplied with the device for safe and efficient supply to charging voltage. You must never employ USB 3.1 or 3 ports for charging vaping device batteries since these ports are designed to supply more than 1 amperage of current. These ports are identifiable by blue plastic coating inside the port vent. It is always advisable to fully charge your device battery before using. It is even true for the devices that allow use while being charged. Using the devices while on the charge is likely to decrease their effective life span.  
oIn case of an improper proportion mix of VG (vegetable glycerin) and PG (propylene glycol), you may experience an accumulation of e-liquid known as gunk. This problem occurs due to higher density of VG (that is like a syrup). More VG in a vaping liquid mix can create this problem. You will need to replace your heating coil and clean the atomizer thoroughly to fix this issue. 
oJust in case the problem is still not resolved, after having cleaned the atomizer (and it still heats up), then the problem is most likely with your vaping style or method. Too frequent vaping or faster vaping can lead to atomizer failure in replenishing your e-liquid quick enough. This can result in damage to coil and lowering of flavor quality. To fix the issue; give your device some rest. It may take about five to ten minutes before your atomizer can replenish and the wick gets wet again.

The problems we discussed in this article are rare occurrences and you can avoid most of these problems by taking care of the few more obvious ones. Where there is no technical failure or mechanical problems with the products, most issues can be avoided by following the safety instruction and maintenance tips that comes with the product packing. It is important to develop good vaping habits and follow maintenance routines regularly. Ignoring safety instructions can result in life threatening injuries and costly damage to your property. It is never smart to take your vaping habits for routine and throw caution to the wind. 
In the end, it is you as a user who has to take care of your vaping device and your personal safety by following safe vaping practices. Misuse of the vaping device will put your device warrant at risk as well. They only replace items that are used in conformance with manufacturer instructions and manuals. Never ignore these instructions for the sake of your safety and proper functioning of your vaping device. Enjoy safe and effective vaping with due regards to instructions.