I have already talked about AGM batteries, which are very good in systems where high currents and a large number of charge and discharge cycles are required. But with all the pleasant bonuses of this technology, it has one problematic point - AGM is significantly more expensive. And the best is the enemy of the good. Due to the pleasant price, relatively better systems in terms of performance, by the way, lead-acid batteries have been relevant for more than 120 years. It is in order to occupy a more budgetary niche of car batteries with a start-stop system, where the requirements for the depth of discharge are not as great as those of AGM, but where the traditional lead-acid battery dies very quickly, and EFB (Enhanced Flooded Battery) was created ...
Let's see if it is possible to downgrade to conventional lead-acid ones, and in what cases, on the contrary, it makes sense to replace the old EFB with AGM.
Spoiler alert: no, it doesn't always make sense to put a more functional AGM instead of a regular battery. Often an EFB or even a regular new battery will be the best solution.
Principle of operation
In terms of chemistry, nothing globally different from traditional lead-acid batteries happens. All the same reversible reaction on plates with the conversion of lead and its oxides to sulfate and vice versa. Sulfuric acid is used as an electrolyte. The key differences are in the layout and composition of the elements.
Firstly, for this type of batteries we use special types of down conductor grid and recipes for active mass. This is necessary in order to reduce internal resistance and energy losses during charging for heating the battery itself during operation. At the same time, the plates themselves are thicker than the classical ones by about 30–50%.
Secondly, the positive plates are enclosed in special envelopes-separators made of extra strong porous plastic based on polypropylene. At the same time, a special reinforcing fiberglass mesh is embedded on the surface of one of the plates. Unlike AGM, where the liquid electrolyte is almost completely sorbed, the EFB still contains free unbound acid. Nevertheless, the packing density is still much higher than in classic lead-acid batteries, and the gaps between the plates are smaller.
Pros of EFB
These batteries have the same problems as the classic ones: they are afraid of deep discharge and storage in such a discharged form, but to a much lesser extent. If we completely discharge an ordinary battery and leave it for a week or two, then large crystals of lead sulfate will begin to form on the surface of the plates. Crystals should normally be microscopic in size for reversible conversion to oxide when charged. In the case of a deep, prolonged discharge, the crystals will change their size, recrystallizing, and continue to grow, breaking the active mass, falling off and crumbling to the bottom of the battery. The largest crystals already lose the ability to completely transform into lead oxide, further reducing the capacitance and increasing the internal resistance. This is how the inevitable degradation of all batteries of this type occurs.
But in the EFB, like in the AGM, the lead plates are covered with fiberglass, which does not allow the active mass to crumble and helps the battery survive a deep discharge longer. In addition to the standard features of this type of batteries, we have added a special carbon additive to the active mass of the negative plates. The technology was named Carbon Boost. It further reduces battery degradation by preventing plate sulfation. Plus, due to its high conductivity, carbon creates something like additional conducting channels inside the active mass. As a result, when charged, sulfate crystals turn into oxide much faster and in a larger volume.
The carbon additive is not a mythical thing like Ostap Bender's Persian powder for bedbugs, but quite a patented, but real compound of a complex composition. The first generation Carbon Boost was specially chemically activated natural graphite, while Carbon Boost 2.0 is a synthetically created high molecular weight compound based on carbon. Who needs to appreciate the beauty of a furious chemical name - search for patents in the open access.
As a result, due to the denser packing of the plates and the additional effect of introducing a carbon additive, we get a battery that can be charged faster with higher currents. At the same time, due to the lower internal resistance, we do not bring the thermal death of the Universe closer by senseless heating of the battery, but we convert the electrical energy into the energy of chemical bonds as much as possible. This is very important for cars with a start-stop system. A conventional battery simply does not have time to get a sufficient charge in the mode of continuous switching on and off of the motor, which is why it quickly breaks down from undercharging.
What to put in place of the old battery
Everything is relatively simple here. It is best to put exactly what the manufacturer recommends, if you have not changed anything significant in your car. For example, they did not install electric heaters for windows, seats, powerful acoustics and other energy consumers that did not come in the original configuration.
The most important rule is not to downgrade. As a rule, the parameters of the battery are calculated with a very small margin, and when you switch to a lower stage, you will receive a lack of starting current, resistance to charge-discharge cycles and guaranteed rapid degradation of the battery. That is, the standard AGM cannot be replaced with a new high-quality EFB, since the peak currents and the number of charge cycles and its speed are still better. Similarly, AGM and EFB cannot be replaced with traditional batteries. They will quickly experience the destruction of the active mass and corrosion of the conductive grids of the grids, if you put them on machines with a start-stop system.
For example, we have the top-end Exide Premium model. This is a classic battery with excellent cold cranking currents comparable to AGMs. But it does not have fiberglass protection against shedding of the active mass, and its resistance to cyclic charge-discharge is several times lower than that of the EFB. It is perfect for replacing the standard battery in ordinary cars, but no recuperation and start-stop will work with it normally.
Can I upgrade? It's a little more complicated here. Within the classic line EXIDE Classic -> EXIDE Excell -> EXIDE Premium you can. Unless just a more powerful battery will cost more. Moreover, you can put an EFB on a regular car and it will work great.
If you had a regular battery
It makes sense to upgrade to EXIDE EFB if you do not like to go under the hood once again and do not want to look there for a few years longer for the next battery replacement. EFB has more charge-discharge cycles all other things being equal.
Upgrading to EXIDE AGM for a regular car, most likely, does not make sense. A higher current than a standard battery will allow your harsh acoustics one and a half kilowatts not to wheeze when, when the maximum current is exceeded, a conventional battery begins to drain voltage by a couple of volts. In other situations, this would be a waste of overpayment. An ordinary car rarely needs so much power, ultra-high currents can help when starting in severe frost, but the price will be significantly higher.
In all other cases, it is better to take the EXIDE Premium with a carbon modification - the same as that of the EFB. It is the most powerful and capacious in the line of classics, degrades more slowly. If you want to save money, take EXIDE Classic or EXIDE Excell to match the class of your old battery. Of course, you don't need to put the Classic on an all-wheel-drive crossover with heated seats and custom acoustics.
If you had an EFB
Change to the same EXIDE EFB of the same class. EXIDE Classic, EXIDE Excell, EXIDE Premium cannot be used! We even add special stickers to AGM and EFB stating that replacement with a traditional battery is unacceptable.
It makes sense to install EXIDE AGM again in the case of powerful additional equipment. Otherwise, you will hardly be able to feel any benefits from a much more powerful battery, even in cars with a start-stop system. If you do decide to install an AGM, be sure to keep in mind that cars with a start-stop system have a BMS - a battery charge controller. It is better to check with the manufacturer if the regular controller can work normally with it.
Not only cars
EFB batteries work almost as cool as AGMs, but cost less. If the price suits you, then you can safely replace outdated traditional batteries in conventional cars. Just remember that although they are maintenance-free, unlike AGMs, they still have free electrolyte. Shake them violently, do not store them upside down.
By the way, according to their characteristics, like AGMs, they should be better suited for the same wind turbines and solar panels with an unstable charging and discharging profile: more currents, more full operating cycles. Although here it is better to use specialized batteries. And also no explosive hydrogen or electrolyte topping up when used correctly.