Comparison of AGM and Lithium Batteries
This article is about lithium and AGM batteries. After the article and video, you will be able to assess which battery type is best suited for your application.
Lithium vs. AGM: Advantages and Disadvantages
Category | Lithium (LiFePO4) | AGM |
|---|---|---|
|
Price |
from 260€ per kWh in our shop |
from 120€ per kWh on the market (from 290€ per kWh in our shop for Deep Cycle) |
|
Depth of discharge |
nearly 100% discharge |
approximately 50% discharge |
|
Weight |
8 - 10 kg / kWh (Li-NMC is even slightly lighter) |
25 - 35 kg / kWh |
|
Discharge cycles |
up to 6,000 cycles (at 80% DoD) |
500 - 800 charge cycles |
|
Service life |
Typically significantly longer than 10 years, after the cycles mentioned above, the batteries still have ~80% capacity! |
Typically around 5 years, depending on care it can also be significantly shorter or longer |
|
Safety |
non-flammable or explosive |
non-flammable or explosive |
|
Recommendation |
Good as drive batteries due to high longevity / charge cycles |
Good as starter batteries due to high discharge currents |
|
Conclusion |
Our clear recommendation is lithium batteries, preferably LiFePO4 - or alternatively Li-NMC |
If you get the AGM batteries for free or only want to drive for a very short time |
Video: Lithium and AGM in comparison
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Particularly for frequent drivers and for tradesmen, a lithium-ion battery should always be the first choice. We mainly use non-flammable lithium iron phosphate batteries.
The lithium battery is ideal if you have little space on board and do not want to add unnecessary weight. For larger applications (10 kW or more) it hardly goes without lithium battery.
.AGM batteries are somewhat cheaper, but significantly heavier and far less durable. For occasional trips and small engines, however, absolutely sensible, especially if the weight and space does not matter.
.If they do not drive so often (<20 times a year) and you do not mind the extra weight on the boat, they can confidently fall back on a cheaper AGM battery. This is especially recommended for smaller engines and if they generally do not need much total capacity. It is important that you use a traction battery for e-motors.
The most significant advantage is a lower price, especially when entering into electric mobility or with a tighter budget, this is very appealing. Note are the storage and charging in the AGM batteries and the lower depth of discharge.
.What types of batteries are there and what are the differences?
There are very many different types of batteries. However, really relevant for use as a boat battery are only a few. We can recommend two different types of batteries that are currently most commonly used on boats.
They all have one thing in common: they are absolutely maintenance-free, leak-proof and safe to handle. Apart from that, they can be installed in any position. Nonetheless, there are some striking differences, from which certain advantages and disadvantages result.
.Facts about lithium batteries:
-
Weight lithium: about 10 kg per usable kilowatt hour
. -
Ideal application: All recreational boats, inflatables, powerboats, frequent boaters
. -
Lithium-ion batteries weigh only about 30% of lead-acid batteries
. -
Lithium-ion batteries can usually be discharged to 100% (80-90% is recommended)
.
Lithium-ion batteries - familiar from the automotive sector - are on everyone's lips. Lithium-ion and lithium-polymer batteries are combined under this term. With lithium-ion batteries weigh only about 30% of the lead-acid batteries (depending on the type different) and also have an extremely high cycle stability and depth of discharge!
Lithium batteries safety
Lithium-ion batteries always consist of several individual cells. Without protective circuits, these are very susceptible to extreme deep discharge or overcharge. Therefore, a battery management system (BMS for short) should always be used for protection.
This prevents the cells from being irreversibly damaged at an early stage, as the BMS prevents deep discharge and overcharging. In most lithium-ion batteries, such a BMS is already integrated and you do not have to worry about anything.
.Facts about AGM batteries:
-
AGM batteries can only be discharged to 50%, our Deep Cycle AGM to 80%
. -
For AGM batteries, the Peukert effect must be taken into account. The capacity is specified on a uniform discharge over 20 hours. At shorter discharge, the capacity drops dramatically
. -
Ideal application: displacer, low capacity, very rare use
. -
Weight gel/AGM: approx. 31 kg per usable kilowatt hour
-
For the same effective capacity already significantly smaller lithium batteries are sufficient
.
Evolution of lead acid batteries
The further developments of lead-acid batteries are gel batteries, in which the acid is encapsulated in a gel. Meanwhile, even more popular are AGM batteries, in which the acid is bound in a fiberglass fleece. Both battery types they are significantly more cycle resistant than a wet battery.
The gel battery is higher in cycle resistance and has a lower self-discharge per month. The AGM battery can deliver higher currents for a short time and is therefore also suitable as a starter battery and is slightly cheaper than a gel battery. Both types are extremely heavy due to the large amount of lead in the battery.
There are large differences within the battery types, especially in the AGM and in the lithium-ion batteries. Some models of AGM batteries can be discharged even 80% (Aquamot) or 100% (Victron Energy). However, the service life should be taken into account.
.For a long time, the lead-acid battery was also used on boats. The disadvantages are obvious: it is heavy, not leak-proof or maintenance-free, and in addition it has a low service life and capacity. However, the biggest advantage of lead-acid technology remains that it is comparatively inexpensive. This technology has been further developed to reduce these disadvantages.
Battery life and depth of discharge
In principle, of course, any battery can be completely discharged, but we do not recommend this. Batteries that are not suitable for this lose particularly strong life or are subsequently irreversibly damaged. There are also usually differences in the charging and discharging currents and other properties, so a comparison between different products may be worthwhile for you. You can always find the product-specific details with the respective articles or in the product comparison.
Capacity and range
When calculating the necessary capacity, we always use the manufacturer's recommended maximum discharge depth to determine the effective usable capacity of the battery. Based on this, the battery is then selected so that you can really drive as far and long as you want.
.The energy density
The energy density of batteries has increased continuously in recent years. Energy densities of up to 300 Wh/kg are now possible for lithium-ion batteries. Typically, however, these are lower at around 120-160 Wh/kg. Lead batteries, as well as AGM and gel batteries have a significantly lower energy density of about 25-30 Wh/kg.
This explains the higher weight of lead batteries at the same capacity compared to lithium-ion batteries.
Batteries can not keep up with gasoline in terms of energy density, however. Gasoline has an energy density of just under 12,000 Wh/kg. Effectively, then, an electric drive always runs on less energy than an internal combustion engine, even though an electric motor is up to 10 times more efficient.
Our recommendation: Lithium boat batteries
Lithium batteries are the best you can use right now. These are light, small and very durable. Above all, the batteries are very safe and can be discharged often.
.Do you have questions about lithium vs. AGM?
Open questions?
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