The following article will explain the general differences between lead and lithium (LiFePo4) (LFP) batteries. Lithium batteries for RVs have been on everyone’s lips lately. But what is so special about this type of battery, and is it as expensive as it seems at first glance? What are the advantages that justify the price?
Let’s compare batteries with water tanks
Imagine a 200-liter water tank. This should symbolize a 200Ah battery. We can fill and remove water here. As usual, with a water tank, it doesn’t matter whether the tank is full, half full, or almost empty. Water withdrawal is possible at any filling level. Filling up to the last drop is also possible without any problems. Nobody would think the water tank should always be full unless you go on a long journey and then use the provisions. But if I can top up the water every day (solar charging), I’m primarily interested in the fact that my daily consumption is fed back into my tank. In winter, my water tank gets a little empty every day due to insufficient (solar) refills so that I can live on my supplies. Every 1-2 weeks, I fill it up again at a tap. And so forth. It’s quite normal. The same is true of a lithium battery!
Now, how is the behavior there with a lead-acid battery?
It almost doesn’t matter whether wet, gel, or AGM is used. The lead-acid batteries always react more or less similar to the problem.
So, we compare our 200 l tank again, only this time, it’s a lead-acid battery. And now comes the major difference! The tank is not empty but contains an absorbent sponge.
Ahh, maybe some will think now – exactly, the sponge brings the following circumstances with it:
We start the comparison with a 100% fully charged tank (lead acid battery). In the beginning, there is no problem, water is fully available, and 50% of the capacity can be removed without further problems. But now comes the difference where the lithium battery differs from the lead acid battery. You can only get to the last 50% of the contents very slowly because the sponge is reluctant to give up the water. Large withdrawal quantities are almost impossible, and the emptier the tank becomes, the more difficult the withdrawal becomes because the sponge is reluctant to release the water. You would have to open the tank and squeeze out the sponge to get the last few liters.
Another problem with this tank arises as soon as it is no longer full: water is deposited at the bottom of the sponge, and the sponge starts to dry out at the top. Do you know the problem of how difficult it is for a dry sponge to absorb water? It’s the same with our tank. If we want to fill it up again after a long time, we can refill the water quickly at the beginning because the lower wet part of the sponge absorbs water well, but the fuller the tank gets, the more you get into the area of the dried up sponge, and it takes forever to fill. The longer the sponge was allowed to dry, the longer it took to fill afterward.
It even goes so far that the sponge dries out irreparably and no longer absorbs water. This is then the sulphation and the associated loss of capacity of the tank (er, the battery).
A battery discharge with immediate charging is not a problem, even with lead batteries.
As with the sponge, it’s no problem if you quickly empty the tank and refill it immediately. The sponge has yet to dry out and still absorbs the water well.
However, the high flow rates, as in a spongeless tank, are not possible due to the sponge. The last 20 liters (10%) can only be filled into the tank very slowly. And precisely, these last 20 liters are the lifeblood of the tank so that the sponge remains absorbent for a long time. The less water I take out of the tank, the longer the sponge will last.
Two tanks or larger tanks are installed to avoid the problem of only 50% being available. So in the end, 200 liters (AH) are available, but with the disadvantage of high weight and more space.
With this example, you can describe the main advantages of the LFP battery quite well and keep a lead acid battery alive for a long time.
This makes the lithium battery affordable.
Surely you now understand why we only use half the capacity of lead-acid batteries for LFP batteries. Because you can use 100% of the battery capacity of a lithium battery, you still have the same usable capacity in the motorhome. As described at the beginning, saving 50% of the capacity also lowers the acquisition costs of the LFP battery.
But the LiFePo4 batteries are more expensive than AGM and GEL batteries.
The initial cost of a 12v lithium battery is higher than that of a lead-acid battery. About two and a half times as high in 2016. If the LFP battery lasts at least two and a half times as long as a lead battery, the costs are balanced, and you get the advantages such as low weight and space savings. Lithium batteries are not that expensive and bring many advantages. If we only compare the manufacturer’s information on the expected charging cycles, it should also be clear to the hard-nosed calculator how illogical lead-acid batteries in motorhomes are. At 50% depth of discharge, a GEL battery makes 700 cycles, while the lithium ion solar battery still has 5000. Even with 100% depth of discharge, Renogy Energy specifies 1000 cycles for its batteries. With this mode of operation, a lead-acid battery dies in the first 40 cycles.
Summary of the facts:
- You only need 50% of the built-in lead capacity if you want to switch to LiFePo4. This results in more than 50% weight and space savings.
- The almost 10 times higher number of cycles results in significantly longer service life.
- The battery can be charged reliably, especially with a solar system.
- A full charge is not necessary with LFP.
- Very high charging efficiency, almost 100% of the energy fed in can also be used again.
- Even the smallest 60Ah or 90Ah LFP batteries can power a 1000W inverter at almost any state of charge.
- Very high charging and discharging currents are possible over the entire state of charge.
- A battery management system is mandatory for the batteries. Depending on the manufacturer, this is already integrated with the battery or connected to the battery separately.
- Due to the flexible end-of-charge voltage, all lead-acid chargers can continue to be used.
- Lithium batteries are intrinsically safe, unlike LI-ION batteries – there is no fire risk.
- Reacts very sensitively to over and deep discharge, only to be used with BMS.
- Above all, LiFePo4 batteries must be installed in the heated area because they cannot be charged below 0 degrees and also lose capacity (at -20 degrees, only 50% of the capacity). With LiFePo4, this effect is no longer so strong.
- The charging current should be limited depending on the alternator and existing wiring. It should be thoroughly checked beforehand which system is used. However, there is more scaremongering than is reported from practical experience. There were no current charging problems with any of the systems I installed.
- Permanent full charging should be avoided. (Remedy creates correct charging technology)
- Determining the state of charge by voltage is very difficult. Installing a battery computer is recommended.
For whom does the lithium conversion make sense?
You can divide it into three groups. A conversion only makes sense for some in the sense of a monetary advantage. The weight savings, or more capacity with the same weight as before, always remains.
Motorhome and campsite users
Those who usually use parking spaces with power columns and only use the built-in batteries for emergency power supply between the sockets will still be happy with lead batteries. With this use of lead batteries, a lifespan of 5-8 years can be assumed. The energy consumed is decisive for the quality of a battery, not the service life in years.
Anyone who is only on the road for a few weeks a year will not necessarily have to use the LFP battery. The lead will continue to be the cheaper solution here.
Freelancers, frequent users, and RV residents
This is where the LFP battery can fully demonstrate its advantages. Low weight, high cycles, and especially in connection with solar systems, where a 100% full charge is often not possible due to bad weather, are excellent arguments for the switch.
Please understand that the battery comparison with a water tank and the sponge is intended to illustrate so that even “non-experts” can understand it. It’s no use bombarding you with electrotechnical terms that probably very few people understand. The readers, who would understand, also need no explanation as to why a lithium battery is so much better than a lead-acid battery.