Lithium (LiFePO4) Batteries are superior, but what happens when you don’t want to replace the AGM lead-acid batteries in your van?
There are so many opinions and rules around batteries. Everything here is a conservative observation after reading many sources.
Why are Lithium Batteries Superior?
- Capacity: The life of an AGM battery is considerably shortened if discharged over 50%. This means a 120 amp-hour battery has only 60 amp hours of usable energy. A Lithium battery can be discharged to 20% without a problem providing nearly 100 amp hours of charge from a 120ah unit.
- Life: AGM batteries are usually good for around 300 to 600 cycles, while lithium exceeds 2,000. A cycle is discharge recharge to an acceptable minimum.
- Weight: Lithium batteries are less than half the weight of AGM. This extra weight is not essential for dual batteries or in a caravan.
- Discharge Curve: An AGM battery drops in voltage over a discharge cycle. For lithium, it is less so – staying above 12 volts most of the way. You will notice this with devices that use an electric motor. Still, the main effect happens when we mix Lithium and AGM batteries, as discussed later.
- Charging: Lithium batteries can charge four times faster to full than AGM if connected to a large enough power source.
- Self-discharge: All batteries, if left unconnected, will slowly lose power. For an AGM battery, this can damage the internal cells over four months. This is why we leave lead acid batteries on a trickle charge when not in use. Lithium batteries self-discharge over a long period and, if left, are not damaged. They have an internal management system that will send the battery to sleep rather than be exhausted to dangerous limits. Waking them up again is not difficult with the suitable DCDC charger.
- Monitoring: Many lithium batteries have wired and Bluetooth connections that allow you to see the battery’s state.
Any Problems with Lithium?
- They are considerably more expensive. At the time of writing, a 120AH lithium is about five times the cost of a 120AH AGM. Given the extra lifetime and power per cycle, lithium still comes out on top – but only if you use your dual battery system often enough to use the long life.
- Suppose you don’t use a specialised lithium DCDC charger for your dual battery system. In that case, the lithium battery life is significantly reduced.
- There are mixed opinions on mixing lithium and AGM on the same circuit.
Why would I mix battery types when towing a van?
It is expensive enough to go lithium for a dual battery system. Upgrading an older van requires changing the charger and the AGM batteries. And that won’t help if you rent or borrow a van.
My Conclusion
I use the KickAss lithium system and have no complaints. There are plenty of suppliers but some do provide a poorer quality product.
The van will have an AC-DC and DC-DC charger. Modern units have solar inputs as well. As long as the car is connected to the van, the lithium battery will provide power to the AGM, keeping it topped up. This means that the lithium will exhaust itself before the AGM drops below full. It will even work without the DC-DC charger. A lithium battery is at about 13.4 volts, so it will not cause the AGM to overcharge.
The van batteries will charge better than if directly connected to the car starting battery. Modern alternators are smart and do not do anything until the battery needs it. You would need an isolator so that the starting battery is never drained.
In Short
Go for it. Plugging your Anderson connection output from your lithium second car battery to your van will work better than any other system.
Please note that this is all hypothetical based on my research. I will let you know in a couple of years if I am wrong 🙂