What Are the Problems with Universal Laptop Chargers and batteries?

I often get asked is it safe to use any of the 3rd party chargers

Mmm.

I must say that I've never been fond of either cheap chargers or cheap batteries.

An underpowered or badly made battery charger / power adaptor can all too easily end up suffering a meltdown and causing a fire.
Lithium batteries fall into the same boat. There are certainly hundreds of sites selling batteries and chargers, but I'd be very cautious about the el super cheapo lithium batteries that you can buy over the net. Badly made lithium batteries, like badly made chargers, can all too readily become an incendiary nightmare.

"How much is your computer worth: €40, €50? The counterfeit power adapters that I've seen are improperly grounded - is that OK for your computer or you personally? The real power adapters meet are necessary international safety and agency compliance standards - do the counterfeit products meet the same threshold.

The real power adapters have over-current, over-voltage, and over-temperature protection...do the counterfeit products have these features.

Is your personal safety and your computer worth more than €40 or €50?"

Moving on: a refurbished power adapter is an especially bad idea. The power adapter case is robustly ultrasonically welded, and cannot be opened without destroying the case. Is the new case of the same quality and is it secured in the same manner than the original. I'd bet not - the ultrasonic welder is specifically designed for the power adapter product, and the refurbisher is probably gluing the casework together. Here's a hint: Apple does not sell refurbished power adapters, and that is for a good reason. 

If you lose or damage your laptop’s power adapter, you may choose to replace it with a universal laptop charger rather than buy a replacement from the manufacturer. Universal models can be cheaper than replacements from the factory, and they may be able to charge multiple devices you own. However, some dangers exist when you use an unauthorized laptop charger that you should consider them before choosing a third-party option.

Voltage

One of the biggest dangers when selecting a universal laptop charger is choosing one that provides the wrong voltage. Power adapters must convert the alternating current from the wall outlet to direct current, and if the charger provides too little voltage, your laptop’s battery will not charge properly and very often too little power can be as bad as too much power for your laptop, can cause problems. Conversely, too high a voltage could damage your battery and your laptop, invalidating your warranty.

Plugs

Different manufacturers use different plug designs for their hardware, making the use of universal chargers somewhat difficult. Many universal kits feature replaceable plugs, allowing you to connect the proper tip for your laptop. You should note when choosing the connector, however, because many plugs might appear identical to the naked eye, but may differ in size by fractions of a millimeter. A plug that is slightly too large can damage the connection, while one that is slightly too small may fall out or provide intermittent power. Also, pay attention to which areas of the connector are positive and negative, as some designs rely on very specific polarity, and will not work if you choose the wrong tip and again can cause damage to your laptop.

Quality

While universal laptop chargers may be cheaper than name-brand replacement parts, in some cases the manufacturers realize those savings by skimping on design quality. Poorly-made adapters may not last as long as the official replacements would, which would require you to replace the hardware again before too long. In addition, extremely poorly-made equipment is a safety hazard, providing incorrect voltage or becoming too hot to the touch to remain safe.

Bottom Line

At the end of the day you get what you pay for, there is that much counterfeit items for sale online you do not know what you are buying.  Remember if there is 40 to 50 euros of a difference in price from a look a like third party adapter or batter from the genuine manufacturers there has to be a difference in quality.  I have seen many’s the computer come in for repair that has damaged motherboards and power connectors all due to faulty batteries and power adapters, so remember buyer beware, only buy from a reputable authorized main dealer that will sell you genuine parts and keep your family safe.  You cannot take a risk with cheap imported items when it comes to electricity your life could be at stake.