The Springers Solar guide to 12V electrics: Lithium batteries

ByRV DailySeptember 10, 2018
The Springers Solar guide to 12V electrics: Lithium batteries

This guide to lithium batteries will give you the pros and cons and tell you why they might actually be the most economic choice

In part one, we looked at 12V batteries in general and just touched on lithium batteries. Without possibly realising it, you have had lithium batteries in your hands for a few years now. Our phones, computers and other mobile devices are all running lithium batteries. Remember your flip phone a few years ago? It was using NiCd (nickel-cadmium) batteries which had issues with memory charge levels. You had to run it almost completely down before you recharged it to avoid problems. Lithium changed all that.

And lithium is changing what batteries we are putting in our caravans, campers and vehicles to run our power-hungry devices. The phone makers never gave you a choice between lithium batteries or other types, they just knew that lithium was the best way to go to give the best service. Deep-cycle 12V batteries are a little different. You have a choice and have to navigate which battery is best for you.

They are more expensive, right?

The first thing you are likely to hear from your mates is how expensive they are. But are they? The upfront cost certainly is more expensive but it is a little more complicated than it seems. You may remember that an AGM battery can really only be discharged 50 percent before you start degrading the battery.
So your 100Ah AGM battery is really only good for about 50Ah before it needs recharging.

If you have a lithium 100Ah battery, you are safely able to get 80 percent or 80Ah out of it before needing to recharge. That is 60 percent more energy out of the lithium compared to an AGM rated at the same 100Ah. If you are comparing upfront costs only, you should be comparing a 100Ah Lithium to a 160Ah AGM.
But wait, there is more!

A lithium battery will recharge more quickly than its AGM cousin. This is important as it means a reduced run-time for your generator or you’d require less sun on your solar panels for the lithium to be recharged to 100 percent. The recharge rate of an AGM battery slows down once the AGM is around 80 percent full while the lithium will continue to charge at the same rate all the way to 100 percent. Out in the field, this is a real benefit.

What’s a charge cycle and why does it matter?

There is another big benefit to lithium batteries. Lithium can have thousands of charge cycles before needing to be replaced. AGM charge cycles are generally limited to hundreds rather than thousands. This benefit will be more important if you use your batteries a lot.

If you only take the camper or caravan out a couple of times a year, the number of charge cycles will be small. If you use your batteries a lot, either by high usage each time you use them or use your camper/caravan many times in a year, then the higher number of charge cycles will be a huge benefit. In these situations the overall cost per cycle will be a lot less for lithium than AGM.

This is where we see lithium making economic sense as well as its other benefits. How you intend to use the battery system will play a large part in determining whether lithium or AGM is the battery of choice.

Charging batteries is not as simple as it seems

Lithium batteries are more sensitive to how they are charged so need to have a specific lithium algorithm available in your DC to DC charger. This is important if you are thinking of upgrading to lithium in your current camper/caravan. Check first if the DC to DC charger is suitable. It is also a factor if you decide to go for AGM now but would like to upgrade to lithium in the future. Again, make sure the DC to DC charger can support both AGM and lithium.

Good quality DC to DC chargers are also important as they may need to accept either solar, generator or vehicle inputs as well as the different battery chemistries. If you intend to charge the batteries using 240V either at home or in a caravan park, you will need to check the 240V charger has a lithium profile.

Checking the state of charge or how much energy is left in an AGM battery is relatively easy. The voltage will equate to its state of charge. A simple state of charge chart will provide this information. A lithium battery is very different as its terminal voltage will remain much the same right through its different states of charge. This means if you hook up a voltmeter to the lithium battery it will always read around 12.8V, leading you to believe it is 100 percent full.

We need to measure the relative amounts of energy input/output to the lithium battery. Thankfully we don’t have to sit there watching the battery all the time; a metal bar called a shunt is connected between the inputs and outputs of the battery and displays this information via a battery monitor. The battery monitor will provide a display of percentage full and may also provide current amount of input or output. This is a good way to check how well the solar panels are working or what the draw is at any particular moment.

Some lithium batteries come with Bluetooth connections that allow you to check the health of the battery while lying in bed in the camper. The State of Charge can be checked as a percentage with information on whether it is charging or discharging, the number of amps and the number of volts. There can also be information on temperature, health and number of charge cycles.

The bottom line

To sum up, lithium batteries have a higher upfront cost but have more available energy for a given energy rated battery. They are much lighter and smaller than equivalent AGM batteries, which is vitally important for your payload consideration. Your intended use will determine whether lithium is more cost effective than AGM, as lithium batteries have a lower cost per cycle over the lifetime of the battery.

If you plan to upgrade to lithium, ensure that you have a suitable charger with a lithium algorithm. Look at your power usage now and future potential before jumping to conclusions on what battery system is best for you.

Words and images Gary Tischer.

You can read all about dual-battery systems here