In the spare parts trade, one can rely on one thing for sure: If the temperatures drop towards the end of the year against or even below zero, the sale of batteries jumps. Because batteries lose capacity in the cold, and a somewhat older specimen, which still serves halfway decently at 20 or 15 degrees, then fails abruptly. The selection of batteries is now quite large.
The AGM Battery
The testers chose for their comparison ordinary car batteries and so-called AGM. AGM stands for Absorbent Glass Mat, which means as much as lead fleece to the USA. In this case, a glass fiber fleece is saturated with sulfuric acid. Unlike normal car batteries, there is no more liquid in the battery, which could leak in an accident, for example. This design brings a lot of advantages. Due to the comparatively low internal resistance of the AGM batteries, the self-discharge is low – the AGM batteries, therefore, retain enough capacity to start even after a prolonged standstill. This is especially important for vintage cars that do not move over the winter, because there must be in the spring otherwise the charger ran. An AGM battery is less susceptible to over-discharge, in addition to providing good capacity at cold temperatures, which is not necessarily the case with normal lead-acid batteries. The lifetime of an AGM battery is higher.
In return, an AGM is less robust when it comes to voltage spikes. In the car, this is not a problem, because the alternator normally does not allow for more than 14.4 volts. But you have to be careful with chargers that must be marked with “AGM” or “Gel.” And such a battery costs considerably more. The tested AGM cost on average more than $200, the average for normal lead-acid batteries was $135.
Advantages of AGM Battery
- AGM batteries have a particularly low self-discharge, which makes charging only every six months necessary unless the battery is stored above 20 ° C.
- They are leak proof and
- They can be installed in virtually any position (observe manufacturer instructions).
- The good cold start values,
- control of the sulfuric acid concentration becomes superfluous,
- There is no consumption of water, which can lead to poor performance and premature failure in conventional batteries.
Expensive, but good
The tested AGM had 70 Ah, the normal car batteries between 72 and 77 Ah. This size, according to the GTU, now also have cars like a Polo or a VW Golf installed ex-factory. A few years ago, such large batteries would have sufficed even in the automotive upper class, but these times are over. The test was based on the criteria capacity, possible cold starts, deep discharge, handling and of course the price. Except for the latter, the more modern AGM batteries have almost only advantages, with these turn out particularly clearly regarding capacity, total discharge and the number of possible colds starts. According to the test, the AGM batteries allow 33 to 24 cold starts, the lead-acid batteries only 23 to 14. This test is carried out in a cold chamber at -20 degrees. Unfortunately, the GTU was also unable to tell us on demand what cold-start electricity is needed to be considered sufficient for a start in this laboratory test. Because of a starter, depending on the engine. To buy an AGM battery you can read the AGM battery review.
The Lead Acid Battery
For the stationary storage of energy, such as a photovoltaic system, the weight does not matter so much. In the house rather bothers that in a lead-acid battery very much dangerous sulfuric acid is used. Therefore, the lead-acid batteries must be stored safely.
If one were to use lead-acid batteries on a large scale, the question arises whether lead can be obtained in sufficient quantity at all. Currently, the world produces 3 million tons of lead per year, with one third coming from China. Theoretically one could save 90 GWh with this amount.
Advantages of lead-acid batteries
- From a purely technical point of view, a lead-acid battery has several advantages. For example, a Bei battery can achieve very high amperages in a concise time, which is why lead-acid batteries are often used in cars as starter batteries. Also, with a lead-acid battery, the state of charge (SOC) can be determined comparatively easily by the acid concentration, since the cell voltage is proportional to the acid concentration.
- From an economic point of view, a lead-acid battery is advantageous, since it is particularly inexpensive to buy due to the relatively cheap use of resources and high production quantities. Also, a lead acid battery is very robust and therefore requires only low maintenance costs.
- Lead batteries have also been in use for many years. If you want to use a lead-acid battery as solar power storage, you can plan exactly how much electricity can be stored at what cost. Longer reference periods, on the other hand, do not exist with the new lithium-ion technology. Therefore, lead-acid batteries are used wherever a long-term predictable and safe storage power supply is desired.
- Also, lead batteries are particularly lightweight and easy to recycle. After all, the fewest know that lead is the easiest recyclable element we know after gold. The recycling procedure of a lithium-ion battery, however, is a technically highly complex and even more expensive process.
On the Other hand, Disadvantages of lead batteries
- As power storage for a photovoltaic system, the lead battery has a life of only about ten years on average. The maximum discharge depth (DODmax) of a lead-acid battery is only about 60 %. A deeper discharge would make the lead battery age faster. To increase the useful life, lead-acid batteries should, therefore, be fully charged monthly and a refresh charge should be carried out several times a year.
- A lead-acid battery has a relatively fast self-discharge. Old, depending on battery type and â € “this can occur at ambient temperatures of 20 ° C up to 30% per month, respectively. At higher electrolyte temperatures, this effect increases.
- Lead batteries also have the disadvantage that they always have to be accommodated in rooms with good ventilation, since when charging smaller amounts of gas arise, which collect in enclosed spaces to a gas cloud and thus represents an explosion hazard.
- Lead-acid batteries are also heavier than lithium-ion batteries and take up more space.