How to select the correct
MEAN WELL Charger & Lithium Battery

1.1 How does a Battery work?

A battery has 2 poles, a positive and a negative pole, depending on whether you charge or discharge the battery, a reaction takes place in which electrons move from the positive to the negative side.

This effect is called a redox reaction (reduction-oxidation), in which the electrons are released from the cathode (reduction) and bind to the anode via an electrochemical reaction (oxidation). This creates a potential difference and electrode current, which can be used to drive a user, such as an electric motor.

These anode and cathode have the largest possible surface area and therefore consist of layers or are rolled up in a cell. The cell contains electrolyte in which the electrons can move freely from the anode to cathode.

1.2 Types of batteries

Basically, there are 3 types of battery, these types are divided into subcategories.

1. Lead Batteries: divided into AGM and GEL
2. Lithium Batteries: divided into NMC, LiFePO4, and the rest.
3. The rest: divided into NiCd and NiMH, among others.

1.3 Lead-acid Batteries

For years, these were the most common batteries worldwide. Most are of the AGM (Absorbed Glass Mat) or GEL type.

With the latter, the electrolyte is incorporated in a kind of gel. The advantages of AGM batteries are the higher discharge currents than what is possible with gel. Because the electrolyte in gel batteries is processed in a gel, the electrons can move less freely. An advantage about GEL batteries is that you can usually mount them in multiple positions (such as upside down), which is usually not possible with AGM batteries.

These batteries can usually be discharged much deeper on a regular basis without high levels of chemical wear. A term you will also encounter is SLA, which means sealed lead acid and does not mean anything other than that these batteries are completely closed and cannot be refilled with electrolyte, which also applies to MF (maintenance free).

1.4 Lithium Batteries

Here we only discuss about NMC and LiFePO4 batteries. There are many other types of batteries that are based on lithium. NMC, or Nickel Manganese, Cobalt Oxide is a very popular chemical compound, commercially strong due to the favourable cost of ownership.

The NMC cells can be supplied as Polymer (LiPo) in the form of a rectangular so-called “pouch cell” and in a cylindrical shape such as the very popular 18650 cell shape, they are then called lithium ion (li-ion) cells. The disadvantage of LiPo cells is the higher initial costs and the lack of a CID (Current Interrupt Device), interrupts the circuit if the cell temperature is too high. This could, for example, occur during charging if the cell is broken. The CID is incorporated in the positive pole of the cell.

LiFePO4 basically has a longer lifespan than NMC due to the lower wear rate, but because the energy density and nominal voltage are lower, you need more cells to achieve the same power as NMC cells. This results in a higher cost price and a larger and heavier battery than what is possible with NMC. The positive point of LiFePO4 beyond its lifespan is the safety attributed to the cells.

1.5 Voltage (V)

Lead-acid batteries have a nicer linear decrease in voltage during use than lithium. Lithium has a flatter curve, roughly between 10% and 90% of the discharge time.

How do we arrive at the voltages indicated on a battery?

To do this, it must first be explained what exactly “nominal voltage” means. This nominal voltage is the average voltage of the battery (the voltage of a battery therefore slowly decreases during consumption). This average voltage is used as the calculation voltage and is called the nominal voltage.

You can calculate this nominal voltage by multiplying the number of cells in series by the nominal cell voltage below.

• NMC (Li-ion/LiPo) 3.6/3.7V
• LiFePO4 3.2V
• Lead acid AGM/GEL 2.0V

Now we come to the voltage indicated on a battery or charger, which is usually an approximation of the nominal battery voltage. So for which type of battery the charger is suitable. This is usually correct with lead/batteries. There are more differences and creative approaches with lithium batteries because the older lead-acid batteries are taken as a reference. For example, 12V can be made very nicely with 2V nominal cells, but with 3.6V Li-ion cells this is of course not possible and 3S or 4S is often used, both of which are called a 12V battery, which is of course not entirely correct.

When a very high power is required from a battery, the voltage of the battery drops at that moment, this is a phenomenon called voltage drop. This effect is caused by the resistance in the battery, so much energy is required from the battery that the redox reaction does not go fast enough. This occurs, for example, when a starter motor in a combustion engine is activated, the required current is so high that the voltage (temporarily) drops.

1.6 Capacity (Ah or Wh)

The capacity of a battery, also known as ampere hours (Ah), is determined by the total surface area of the anode and cathode per cell and how many of these cells are in parallel.

Suppose the cells in the above diagram have a capacity of 10Ah each, then the total capacity is 10*4= 40Ah. If the cells in this example have a voltage of 2V, the voltage of the entire system remains 2V.

Although capacity is often expressed in Ah, it is more accurate to express the capacity of a battery in Wh (Watt hours), or Voltage (V) * Ampere hours (Ah). This applies in particular to all batteries that are not based on lead acid or 1.5V penlites. For all other forms, including lithium, the voltage is often rounded to an equivalent lead-acid battery variant.

As an example; take a 12V 10Ah lead battery and a 12V 10Ah li-ion battery. You would initially say that the capacity of both batteries is the same. The capacity of the lead acid battery in Watt hours is 12*10 = 120Wh. For the lithium battery you must first know whether this is a 3S or 4S version to approach 12V, after all 3*3.6V = 10.8V and 4*3.6V = 14.4V. In other words, 12V cannot actually be simulated well with li-ion cells, yet it is offered. Let’s assume it’s 4S. Then the sum becomes 14.4V*10Ah is 144Wh. Basically more effective than the lead battery, and then we leave the Peukert effect aside.