Lithium batteries are cheaper than lead-acid batteries

In this article we will show that a lithium battery is already cheaper than a lead acid battery when you compare the costs over the period of use.

Why is that?

Let’s start first with the usable capacity of lithium and lead-acid batteries. With a lithium iron phosphate battery you can use about 90% of the actual capacity. Since this actual capacity, for example in the case of a Liontron battery, is on average approx. 8-10% above the nominal capacity, this results in a real usability of 100% of the nominal capacity on average.

With a 100Ah AGM lead battery, you can only use half of the nominal capacity (i.e. 50Ah) if it is to be used for around 1000 cycles. It must be taken into account that the AGM battery can only do this if it is regularly recharged up to the end-of-charge voltage immediately after discharging. This means that a 200Ah lead battery is required to achieve the same capacity as a 100Ah lithium battery, since the AGM battery can only use 50% of this capacity to protect the battery. Unfortunately, because these rules are often not observed in practical use, many AGM batteries are often so weak after only 1-3 years that they have to be replaced.

Efficiency

While a lithium battery can use 96-98% of the energy fed in productively, this is only around 85-88% for the AGM battery. The difference is turned into heat and lost.

As a result, you need a lead battery with a capacity of more than 200Ah (namely approx. 220Ah) in order to permanently use the same amount of power as a 100Ah lithium battery. Due to the higher efficiency, when using lithium technology, less PV power is required on the roof to generate a comparable usable amount of electricity.

Cycle comparison

However, there are advantages in particular with regard to the number of possible charging and discharging cycles. This is the discipline in which the lithium battery mercilessly beats every lead battery to the wall. After about 1000 cycles at 50% depth of discharge, a high-quality AGM battery only has about 80% of its original capacity. This also only applies under the condition that it never remains in a partially charged state for more than a few hours.

A lithium iron phosphate battery, on the other hand, largely maintains its charging capacity for up to approx. 3000 charging cycles. After that, it still has 80% of this original capacity and can easily be used for another 7000 cycles if the remaining capacity of around 60% is sufficient. This is the reason why lithium batteries can lead a second life, e.g. as electricity storage in the house, after their use as drive batteries in the car. So if we compare the cycle life of the two technologies, the lithium battery is at least three times superior to the lead battery.

This means that we have to buy three 200Ah AGM batteries for around 450 euros each to achieve the cycle life of a 100Ah lithium battery.

The weight

Another advantage is the lower weight. A 100Ah lithium battery weighs between 13 and 15 kg. A 200Ah AGM battery easily tips the scales at 55 – 60 kg. If the lithium battery is installed in a mobile system (e.g. in a mobile home), the fuel savings over a 10-year vehicle life will be enormous, depending on the mileage in kilometers.

Discharge

With regard to the possible short-term current draw, a lead-acid battery is still superior when a large amount of current has to be drawn for a few seconds to start an engine in the car. Up to 1000 amperes for seconds are common there.

Therefore, lead-acid batteries are likely to survive for a long time as starter batteries. However, if there is a high current draw over a longer period of time, the voltage of a 12V lead battery, for example, drops very quickly to 11 volts and lower.

If an inverter with 1,600 watts AC power is connected and this power is required for a hotplate or a coffee machine, for example, then the inverter draws 1,500 watts: 12 volts = 130 amps. If the approx. 10% conversion losses of the inverter are taken into account, the total power requirement is approx. 143 amps, which the battery must provide permanently.

Even with a 100% fully charged 200Ah AGM battery, the voltage falls below 12V and below after a short time at 143 amp discharge, whereupon the inverter switches off due to undervoltage. In contrast, a 100Ah LiFePo4 battery such as the LIONTRON LX can continuously deliver 150A without the voltage dropping below 12V.

Carging the battery

A lead-acid battery requires a multi-stage battery charger, which charges the battery with different charging stages such as main, trickle and equalization charging. The charging voltage also depends on the internal temperature of the battery. Good lead-acid battery chargers are therefore equipped with an external temperature sensor that should be permanently mounted on top of the lead-acid battery. As we know, a lead-acid battery should be fully charged as soon as possible after the current has been drawn off, if it is not to die prematurely due to sulphation much earlier than planned.

This good care is z. B. easily possible with a solar system in summer, but difficult to achieve in winter. When using a lead-acid battery, we recommend our customers to connect it to an automatic charger for the longest possible service life during the winter months, so that the battery is cared for to prolong its life.

You also have to know that fully charging a lead-acid battery (from approx. 11V (empty) to approx. 12.8V (full) can take 12 hours or longer. The battery initially takes up a very high charging current and can be charged quickly However, the current then decreases rapidly as the state of charge increases, so that the last 50% of the charge takes significantly more time than the first 50%.

Since a lead-acid battery has to be kept between 50% and 100% state of charge, as already mentioned, it can only be charged slowly, since in this state range between 50% and 100% of the total capacity the battery can only absorb relatively little current per unit of time, itself if the charger or the solar system could provide a higher charging capacity.

It can also take up to 18 hours until the end of charging, when the battery only absorbs a few milliamps. However, it is precisely this point of absolute full charge that should be reached regularly in order to avoid harmful sulphation and to achieve an acceptable service life for the lead-acid battery.

A lithium battery can be fully charged with a constant charging current in around two hours, provided the charger is powerful enough. Everyone knows this today from their mobile phone. No complicated charger is required, but it can be charged continuously with main charging and constant current. Modern LiFePo4 batteries like the Liontron can be charged with any 12V lead charger with an end-of-charge voltage between 14.2V and 14.6V. Even an ancient 13.8V charger from the first generation of 12V gel batteries can charge a lithium battery. It is only fully charged up to 90%, for example, but this does not damage the battery at all.

For practical use, e.g. in a mobile home, this means that the vehicle’s alternator can recharge the lithium battery that was consumed during the night in a very short time, even during a short morning drive to get a roll. However, this would require a charging booster that supplies the lithium battery with a sufficiently high charging capacity from the “chronically lazy” vehicle alternator as soon as the vehicle engine is running.

A lithium battery feels most comfortable when it is partially charged. This means that regular full charging, as is the case with lead-acid batteries, is not required and does not extend service life. If the battery is not used for a long period of time, it should be stored half charged and it can be used again after a year without damage. If there is Bluetooth monitoring in the battery, it should be recharged about every six months, because this device permanently consumes a few milliamps of electricity.

Monitoring & maintenance

Offene Flüssigkeits-Bleibatterien benötigen eine regelmäßige Kontrolle und Wartung. Bei jedem Ladevorgang entweicht Wasserdampf, welcher als destilliertes Wasser nachgefüllt werden muss. Verschlossene Bleibatterien wie AGM oder GEL benötigen keine Pflege, sondern lediglich Überwachung der Abschaltung bei ca. 50% Entladung, sowie möglichst sofortige Vollladung nach jeder Entladung. Generell raten wir Kunden, die eine Bleibatterie einsetzen zum Einbau eines Batteriemonitors. Es zeigt vergleichbar einer Tankanzeige für Batterien den Ladezustand in Prozent, den Lade-/Entladestrom und die Batteriespannung an. Ein System von z.B. Victron mit Bluetooth Anzeige kostet rund 200 Euro und ist den Kosten für eine Bleibatterie hinzuzurechnen, wenn man diese mit einer Lithium-Batterie vergleicht.

Eine Lithium-Batterie hingegen muss nach der Installation für viele Jahre gar nicht gewartet werden. Das in jeder Batterie eingebaute Batteriemanagement-System (BMS) sorgt dafür, dass die Batterie vor jeglicher Fehlbehandlung geschützt wird. Es schaltet die Batterie bspw. bei Unterspannung und Überlastung ab und sofort automatisch wieder ein, sobald das Problem behoben ist.

In vielen Lithium Batterien sind Bluetooth Batterie Monitor-Systeme in Form einer Handy APP verbaut. Diese zeigen dem Anwender neben dem Ladezustand in Prozent auch den aktuellen Verbrauch, die Anzahl der bereits verbrauchten Zyklen sowie die Einspeisung an, die gerade von der angeschlossenen Solaranlage, vom Batterieladegerät oder der Lichtmaschine in die Batterie geleistet wird.

Safety

Lead-acid batteries, even those that are closed, emit so-called oxyhydrogen when charged with too high a voltage, which can be caused to explode by a spark. Therefore, they may only be installed in well-ventilated places. Lithium iron phosphate batteries, on the other hand, neither burned down uncontrollably nor exploded when tested, even when fired on with bullets. They are considered the safest and most durable lithium technology.

Temperature behavior

Bei tiefen Temperaturen können Bleibatterien für kurze Zeit immer noch hohe Ströme abgeben. Dies aber wirklich nur für kurze Zeit. Dadurch kann man auch bei -40°C noch ein Auto starten. Allerdings nur, falls der Motor sofort anspringt. Wiederholte Startversuche quittiert die Batterie mit Versagen, da die Kapazität einer Bleibatterie bei sehr tiefen Temperaturen von -40 Grad bis auf 15% ihrer Nennleistung sinkt. Lithium-Batterien verfügen selbst bei sehr niedrigen Temperaturen bis -40°C noch über rund 80% ihrer Kapazität. Allerdings können die LiFePo4 Batterien bei Minustemperaturen zwar entladen, jedoch nicht geladen werden. Aus diesem Grund sollten LiFePo4 Batterien in sehr kalten Gegenden auch nicht im Freien verbaut werden.

Conclusion

Lead-acid batteries have lost their raison d’être in cyclic applications as service, traction and solar batteries. They are inferior to modern lithium technology in almost all technical respects and now also in financial terms as soon as the costs for the period of use are taken as a basis. Only as a starter battery and as a drive battery in forklifts will this technology remain for some time. The main reason for the success of lead-acid batteries in starter batteries is the low investment and the fact that the battery is only discharged by a few percent during the starting process and is then immediately recharged by the alternator after the engine has started. This allows it to serve well in this application over a period of a few years. It is similar with a forklift, where the high weight of the lead battery is an advantage and the battery can be recharged all night after an 8-hour day of use.

For the user, the biggest difference between lead and lithium is the completely hassle-free practical application. It hardly matters anymore whether the battery is full or half full or whatever.

Just like with a cell phone, the battery simply shuts down when it hits a low level and wakes up immediately when it’s recharged.

Source: Liontron

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