Choosing the right battery

“If you buy cheap, you often buy twice”

What is the difference between inexpensive and cheap? This question worries almost everyone who wants to buy something new. It almost doesn’t matter how big the purchase is. Price is almost always an important factor in everyone’s decision-making process.

This decision-making process is all the more complicated the less familiar you are with the product and/or service. It becomes all the more difficult when it is a cost-intensive matter.

The Internet marketplaces are full of various offers for different batteries, and since thelithium phosphate battery is one of the most expensive components in a pedelec, along with the motor, we would like to shed some more light on the cost structure of a battery at this point.

  1. The battery cells – depending on the configuration of a battery, the battery cells are connected in series (increase in nominal voltage) and in parallel (increase in capacity). For example, a 36V battery has 10 battery cells in series. If the nominal capacity of the battery is 13Ah and cells with a nominal capacity of 2.6Ah are installed in the battery, we are talking about 5P, i.e. 5 battery cells, each with 2.6Ah, which are connected in parallel. Without having completed a math degree, anyone can calculate 10 x 5 = 50 battery cells, these are built into the battery.

The battery cells make up about 60 – 70% of the total cost of a battery. If these come from well-known manufacturers such as Panasonic (Sanyo), Samsung SDI, LG Chem or Murata (Sony), the total price for the battery cells is already above the price of some dubious suppliers.

  1. The BMS (Battery Management System) – the BMS is the controller, in other words the brain, of a battery. The BMS ensures that the battery is not overcharged or over-discharged. The BMS controls how much current the battery can pass on to the controller, but also how much charging current the battery is supplied by the charger. Furthermore, the BMS, like a conductor in an orchestra, also ensures that all built-in battery cells are in a similar voltage level.

A Smart BMS is a further development of the control component. We speak of Smart BMS when it is programmable and can ensure additional functions such as communication and other monitoring. A smart BMS is usually more accurate and more expensive than a so-called standard BMS.

  1. Housing, case and the like – many batteries are installed in housings. These can be special housings for pedelecs that can be mounted on the frame, luggage rack, etc.

  1. Welding Material – Nickel is commonly used to connect the battery cells together in series and parallel. The purer the nickel, the more durable and conductive this material is. To save costs (nickel is quite expensive), cheaper nickel alloys are often used. HILUMIN is an example of a nickel coating on steel. The price of this material is much cheaper compared to pure nickel.

  1. Labor – Depending on where the battery is manufactured, different labor costs will factor into the price of the battery. Manufacturing in Germany, for example, is much more expensive than in China, for example.

A very common, we need to be serious about choosing solar battery, under-discussed issue (in our opinion) is the relationship between price and lifespan. Batteries are rechargeable and therefore the price of the battery must be calculated over its lifetime. In practice, the price is calculated in Wh (watt hours). Wh is the amount of energy stored in the battery (capacity x voltage). So you divide the total price into the total amount of energy to know how much a watt-hour costs.

Calculation example:

  • A 36V battery with 10Ah has 360Wh and costs €200. The price per Wh is therefore €200 / 360Wh = €0.55 per Wh.

  • Another 36V battery with 20Ah has 720Wh and costs €350. The price per Wh is therefore €350 / 720Wh = €0.48 per Wh.

So which battery is cheaper?

Now let’s try to make it a little more complex… suppose you have a 36V 10Ah battery from U.S. for 150€ and the battery is no longer usable after a year. A comparable 36V 10Ah battery costs €300, for example, and lasts 3 years.

Which battery did you pay more for?

In our many years of experience, there are very few bargains on rechargeable batteries. Anyone who manufactures with branded battery cells pays almost the same prices for the battery cells in Germany, the USA and China. Since the price of the battery cells in the battery is the main cost factor, the more cost-effective production in Asia cannot justify serious price differences. Caution is the order of the day here!

One of the most frequently asked questions is: what is the best battery cell for a pedelec battery? There is no clear answer to this question.

There is a large number of different Li-Ion battery cells from different manufacturers on the world market. Since so-called cylindrical Li-Ion battery cells (mainly in the formats 18650, 20700 and 21700) are mainly installed in the batteries of pedelecs, in this article we will try to list and explain the differences between common battery cells.

The following figure shows the differences between 3 common chemical compositions of Li-Ion battery cells (anode and cathode) as an example of the complexity. 6 properties are used. Each of these “families” includes many different “relatives”, i.e. different Li-Ion battery cells.

If you plan to store the power in the solar panel in a battery for use in the event of a power outage. You need to go through the solar panel calculator to calculate how many watts of solar panels and how many lithium batteries you need to install.

In our article we will mainly deal with battery cells from the 4 largest manufacturers in the world, Panasonic (Sanyo), Samsung SDI, LG Chem and Murata (Sony). We disregard the numerous manufacturers of Li-Ion battery cells from China, because in our opinion they cannot compete with the products of the above-mentioned manufacturers in terms of quality.

In our list we take into account the battery cells that we use the most. Our evaluation is based on the manufacturer’s technical data and on our own experience with the battery cells. We use criteria other than those in the figure above and evaluate on the basis of three levels. + stands for good, ++ stands for very good and +++ stands for excellent.

Explanations and additions to the table:

1. Most of the listed values are based on the technical specifications of the manufacturers.

2. The internal resistance roughly characterizes the changes in an electronic component under load. The lower the value, the more robust the battery cell (the voltage drop is lower).

3. The continuous load is not standardized by the manufacturers.

4. There are sometimes different data sheets with sometimes different values for the same battery cells. Since we cannot find any reasons for this, we assume possible explanations:

a) Manufacturers continuously improve the quality and performance of their products.

b) There are actually different modifications of a battery cell for different applications. We therefore assume that a type X battery cell can have different characterizations in application A than in application B.

5. The service life of a battery cell (cycle life) is determined by the manufacturers under different conditions calculated (charging, discharging, temperature etc.). Basically, the service life is understood as a complete cycle from completely empty (end-of-discharge voltage) to completely full. It is important to add here that both the BMS in the battery and the controller in the pedelec switch off earlier than the end-of-discharge voltage battery cell. The consequence is not only the extension of the service life of a battery, but also the low, real usable amount of energy (Wh).

Since the battery cells also differ in price, the selection of the most suitable battery also depends on the total price of the battery.

As you can see, we can never talk about the “best” battery, but always about the “most suitable” battery for a specific driver profile. If you plan to build your own solar system, just in case you need it. You should know about the federal solar tax credit, it can really save you a lot of money.

If you use your pedelec in winter, you will probably use a battery with different battery cells than someone who only rides in summer. Anyone who rides routes with a lot of inclines will probably choose a battery with different battery cells than the pedelec rider who rides in a rather flat landscape.

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