Anyone living in the 21st century has likely been caught in a situation where their mobile phone is about to die at the most inopportune of times. If you have a power bank, then you can generally heave a sigh of relief and just plug it in, but what if the power bank you thought had a full charge can\u2019t do its job when you need it to?\n\n\n\nYes, any power bank will lose charge over time, so your power bank's quality is paramount. A high-quality power bank can keep its charge for many months without any losses. In contrast, a low-quality power bank can start losing charge within as little as a few weeks.\n\n\n\nThis article will explore what power banks are and how you can manage self-discharge.\n\n\n\nA Word About Power Banks\n\n\n\nA power bank is essentially a reusable battery. It is loaded with charge using a USB charger to provide power to other battery-operated devices. Power banks can also be referred to as portable chargers.\n\n\n\nOver the years, and as technology advanced, several different power bank types and makes have become available. The size or capacity can classify a power bank as you would need an output of roughly 16 to 20 volts to power a laptop, while the average power bank, used to charge smaller devices, typically has a 5-volt output.\n\n\n\nOther important classifications are the charging method and the charge delivery method. The standard\/universal power bank is generally used as outlined above. They are the oldest type of power bank on the market and obviously the most commonly known.\n\n\n\nSolar power banks use built-in photovoltaic cells to charge in addition to the normal USB charging method. This can be a great feature when you are camping or far away from traditional power sources.\n\n\n\nThe solar panel is quite small on solar power banks and will require really bright and sunny days for the solar panels to charge the power bank adequately.\n\n\n\nWireless power banks have developed in conjunction with other devices\u2019 wireless technology. They can be charged traditionally and then deliver charge wirelessly to a compatible phone or device. \n\n\n\n\n\n\n\n\n\n\nFeatures that Influence the Quality of a Power Bank\n\n\n\nRegardless of the type of power bank you have, it is still just a rechargeable battery. The same characteristics and safety precautions that apply to batteries will apply to your solar charger with some minor changes here and there. For the most part, power banks are either lithium-ion (Li-ion) or lithium-polymer (Lipo) batteries.\n\n\n\nThe basic workings of the two batteries are the same, but one's polymer nature has a big effect on the quality of the power bank.\n\n\n\nHow Lithium-Ion Batteries Work\n\n\n\nThese batteries make use of lithium's electrochemical potential as its value is very high and is a very reactive metal. It is used in a metal oxide within the battery as it\u2019s very stable in such a construction.\n\n\n\nThe battery has a cathode (+), with the metal oxide, and an anode (-), usually made of graphite. There is an electrolyte (fluid) and a separator (permeable membrane) between the two terminals. Both the electrolyte and separator serve as substances that do not allow the flow of electrons.\n\n\n\nWhen the battery is charged, the lithium atoms in the metal oxide are removed. It is unstable\/reactive, able to lose an electron with a negative charge.\n\n\n\nWhat is left is free lithium ions with a positive charge. These ions will flow through the electrolyte and separator as it is attracted to the negative anode and collected in the graphite. \n\n\n\nThe electrons will then move through the external circuit and collect in the graphite on the anode side. The graphite does not facilitate any reaction and is just a storage medium for the separated lithium ions and electrons. Once this reaction is complete, the battery is fully charged (source).\n\n\n\nWhen a load is attached, the battery discharges, and the opposite happens. The electrons move back through the external circuit, and the lithium ions flow back to the cathode through the electrolyte. They are then integrated back into the metal oxide. \n\n\n\nElectricity is provided to the load when this process takes place, and heat is also released, which causes a power bank to become physically hot to the touch. A charging cycle is now completed, and you can reconnect the battery to a power source to charge it again. \n\n\n\nHigh temperatures can cause the electrolyte fluid to dry up, which could cause an internal short circuit, potentially leading to an explosion and fire. The separator is built-in to prevent this. \n\n\n\nLipo batteries work the same as Li-ion batteries, but rather than a liquid, it has a gel-like substance as an electrolyte, which greatly influences its list of pros and cons. \n\n\n\nLithium-Ion vs. Lithium-Polymer Batteries \n\n\n\nOne of the essential differences between the two batteries is the price point. Li-ion batteries are cheaper than Lipo batteries, even though the latter has become very popular. Its popularity is likely to lead to their mass production, which will eventually bring down its price. \n\n\n\nLipo batteries are safer than Li-ion batteries as the gel-like electrolyte is less likely to leak and less likely to have thermal runaways. They\u2019re also more versatile and can be made into almost any shape.\n\n\n\nIn the absence of heavy metals and fluid electrolyte, it is lighter than the Li-ion battery. Lipo batteries also have a lower self-discharge rate than Li-ion. \n\n\n\nUnfortunately, Lipo batteries have a low power density. In other words, it simply stores less power than a Li-ion battery of the same size. It also has a shorter lifespan as the electrolyte hardens over time. \n\n\n\nIt also suffers from the memory effect, which means they cannot fully recharge if they are only partially discharged over and over again. \n\n\n\nLi-ion batteries have a higher power-density than Lipo, and they have a longer lifespan with 300\u2013500 possible charge cycles. \n\n\n\nUnfortunately, their power-density doesn\u2019t stay the same, and its efficiency decreases as it ages. Li-ion batteries are a bit more of a safety risk since they\u2019re less robust and more prone to experiencing explosions or fires (source). \n\n\n\nWhat Should I Look For in My Power Bank?\n\n\n\nThe type of power bank you buy will very much depend on how and why you want to use it. The Li-ion battery is not as safe as the Lipo, but the likelihood of having a power bank without protective circuitry is slim to none. \n\n\n\nThis circuitry should prevent overcharging, over-discharging, and other issues that could cause it to explode or catch fire. \n\n\n\nIf you\u2019re working on a budget, a Li-ion power bank will cost less, and it will probably be smaller or thinner while providing you with more power than a Lipo battery. \n\n\n\nIf you are potentially going to travel a lot, and your power bank might need to endure some rough-and-tumble situations, a Lipo battery is a much better choice. It can provide the same power as a Li-ion battery but will be larger. On the other hand, it is also more robust and lighter. \n\n\n\nAbout Self-Discharge\n\n\n\nAny power bank will suffer some degree of self-discharge. Self-discharge is a natural chemical process that you cannot completely avoid, and there are several factors that can influence a power bank\u2019s self-discharge rate. \n\n\n\nBatteries stored at higher temperatures self-discharge faster, and, if there are impurities in the electrolyte or the electrodes are chemically unstable, it can also self-discharge faster. \n\n\n\nIn general, lithium batteries self-discharge at a lower rate than other batteries, and Lipo batteries at an even lower rate than Li-ion. It can even be as low as 1% per year. \n\n\n\nHow to Protect My Power Bank\n\n\n\nAlthough you cannot completely avoid self-discharge, you can do a couple of things to ensure that your power bank is working optimally. \n\n\n\nMake sure you purchase a high-quality product. This should ensure that you get the best possible battery without the above-mentioned problems that can accelerate self-discharge. \n\n\n\nAn important step is to always store it at a low temperature. Keep it out of the sun or areas that get very hot. The heat will increase the self-discharge rate, and this change in temperature can also contribute to the battery possibly exploding or catching fire. \n\n\n\nChoose carefully when buying a power bank and know your product. If it might be exposed to damage from being dropped, choose a Lipo power bank that will better withstand impacts. Also, make sure that the power bank comes with safety features that will prevent overcharging and over-discharging (source). \n\n\n\nFinal Thoughts\n\n\n\nThe charge and discharge of a battery is a chemical process, and self-discharge is also a natural chemical process that takes place that you cannot completely avoid. \n\n\n\nThe two main batteries used in power banks have very low self-discharge rates. Properly caring for and maintaining your power bank can also reduce the self-discharge rate.