Updated 9 May 2017
Lithium-ion batteries in caravans and motor homes pack a lot of energy but need specialised knowledge to use safely and reliably. Here’s how and why – and how to install and use them.
Lithium-ion batteries in caravans and motor homes work well for those who free camp. They also lighten overweight RVs. All supply high peak power yet can also be used as deep cycle batteries. Their chemistry and working is very different from traditional batteries. They are almost a different species.
Energy and power are not the same
Ongoing promotion suggests lithium batteries have more power. This does not, however, mean they have more energy. Energy enables work to be done. Power relates to how fast energy is used. For example, the energy needed to start a big 4WD is tiny. It’s about that drawn by a 5 watt LED in an hour. But that 5 watts is used in a second or two. It consequently demands a lot of power.
Conventional deep cycle batteries are no match for lithium ion’s ability to power such loads. But, if weight is no issue, a plus 300 amp hour AGM bank is adequate for RV use. It lacks LiFePO4’s potential power, but such power has no value unless needed. Why pay for power you don’t need?
Lithium-ion batteries in caravans and motor homes – battery types
Lithium cobalt oxide (LiCoO2) batteries store the most energy. In 2013 however, one started a fire in a Boeing 787. United Airlines reported two more a day or so later, grounding all 787s for a time. These fires made headline news. The lithium-ion batteries (LiFePO4) in caravans, however, have very different chemistry.
This LiFePO4 battery is claimed to chargeable good quality two-stage battery chargers, The battery management system (see below) is inbuilt.
LiFePO4 batteries are less energy efficient. They can ignite but the material used must exceed over 10000 C to do so. They are thus close to fire-proof. At about 105 watt hours/kg they are about a third the size and weight of lead acid batteries of similar capacity. They are claimed to be non-toxic, however waste recovery experts claim recycling issues.
This graph shows the typical (per cell) voltage during discharge. That most probable for an RV is slightly above the blue line. (That shown by the red line is of extremely high constant discharge. It does not apply to caravan and motor home use.)
Lithium-ion batteries in caravans and motor homes – available current
Unlike a lead acid battery’s, LiFePO4 voltage remains almost constant. It is typically 13.1-12.9 volts for RV use. It drops steeply at 10% or so remaining. LiFePO4s suffer damage or shorter if fully discharged. Some claim they are ruined as a result. Discharge must thus be limited. This is done by an associated battery management system.
Close to constant voltage virtually eliminates low voltage fridge issues, likewise lights dimming. It also assists solve issues with RV 230/12 volt converters. See Electrical Converter Problems in RVs-update.
Batteries differ in their ability to supply high current loads over time. Here, deep cycle lead acid batteries are very limited. Gel cells and AGMs are less limited, but lithium-ion excels. A LiFePO4 18 Ah jump starter reliably supplies starter battery level current. It furthermore serves as a short term deep cycle battery.
Lithium-ion batteries in caravans and motor homes – safety
LiFePO4s can and do release massive current. Never short circuit their terminals – resultant instantaneous current flow vapourises whatever caused it. Wear safety glasses and protective clothing when working on or near such battery, particularly these.
Install circuit breakers as close to the battery as possible. Rate these for the safe current the cabling may carry. In the event of a short circuit, this safeguards against burning or melting.
Unless charged/discharged at more than triple their amp hour capacity, lithium-ion batteries rarely vent gas. Venting may, however, occur above that. Their makers claim emissions are neither toxic nor explosive. It is nevertheless advisable to ventilate them in order to limit heat build up.
Most LiFePO4 batteries have a recommended working range of -18 degrees C to about + 40 degrees C.
Lithium-ion batteries in caravans and motor homes – cell monitoring is essential
The upper safety limit of a LiFePo4 cell is 4.2 volts. If a 12 volt LiFePO4 battery charging at 14.4 volts were to have three cells at a safe 3.2 volts, the remaining one has 4.8 volts across it. That cell heats up. It may ignite or even explode.
Another risk is of an unbalanced cell’s ongoing discharge causing remaining cells to reverse that cell’s polarity. Subsequently attempting to recharge (warns EV Australia) ‘carries a significant risk of catastrophic failure’. A cell management system prevents this. It may be within the battery housing, or external.
The more cells series-connected, the greater the risk of unbalance. Generally, the larger the cell capacity the greater the risk of catastrophic failure. Whilst charging (and in use) the higher the charge and discharge current the greater the risk of cell unbalance.
Control of charging and discharging voltage and current is also essential. This may be done by the battery management system, or the battery charger. LiFePO4 cell management is essential – but nevertheless not necessarily supplied.
Lithium-ion batteries in caravans and motor homes – charging
Many LiFePO4 users have strong views about charging. All regard cell management as vital. Most agree that discharge be limited to about 10% remaining. Not all agree about the final state of charge, specifically how close to 100% charging is safe.
This graph shows the relationship between charging voltage, current and a typical LiFePO4’s state of charge.
Most agree a 12 volt LiFePO4 is safe to charge to 80%-85%, at a constant 13.6 volts. Many DIY users do just that. If then discharged to 10%, usable capacity is 70%-75%. The LiFePO4 industry conversely maintain that deeper charging enables safe use of close to full capacity. The approach typically charges, at constant current, to about 90%. It then switches – to applying 14.6–14.65 volts. Doing so, however requires accurate control. Moreover, it’s surprisingly hard to measure accurately and consistently. It is harder still to control it.
Of charging efficiency, LiFePO4 is way ahead. Vendors claims of 92.5-95% are probably true – that of lead acid batteries is about 80%.
Lithium-ion batteries in caravans and motor homes – usable lifespan
Battery life is industry defined as cycles drawable before capacity falls to 80% of that when new. This closely relates to ongoing depth of discharge with conventional batteries. Some users and vendors, however, claim that LiFePO4s (in RV usage) are barely affected by discharge rate or depth. Many discharge to 20% or less remaining, however some claim this limits lifespan.
Most vendors claim about 2000 cycles if discharged to 20% remaining (almost regardless of load).They suggest life is extended by limiting charge to 90%. Not all LiFePO4 chargers, however enable this.
LiFePO4 batteries usage only reached largish scale around 2012. Claimed lifespan is thus based on speeded-up cycling, and speculation. There can be no proven real-life data until until 2022 or so.
Lithium-ion batteries in caravans and motor homes – battery chargers
Some lithium-ion battery makers advise that, given battery monitoring/charge control, all required is a two-stage charger. Many users disagree. They do, however, generally accept that dedicated LiFePO4 chargers are safer.
Lithium-ion batteries in caravans and motor homes – alternator and/or solar charging
Many users claim (for LiFePO4 charging), ‘normal alternator charging’ is fine. This cannot be. There has been no such thing as a ‘normal alternator since 2000. From thereon alternator outputs began to vary, from 12.7 volts to plus 14.7 volts. Many have voltage that varies with load and/or temperature. Some now have voltage that varies from plus 15 to 12.3 volts. Or even none at all at times. Only a few LiFePO4 batteries are promoted as drop-in replacements.
Redarc and Sterling etc, produce alternator chargers specifically for LiFePO4. Or with a LiFePO4 setting option. Such chargers include under/over voltage protection and cell balancing. Some also accept solar input. They stress such units only be used with LiFePO4 batteries that they approve.
The (Australian designed and made) Redarc LFP 1240 alternator. It charges a LiFePO4 12 volt battery at 40 amps. It also accepts input from solar modules. Pic: Redarc.
LiFePO4 alternator chargers should be located close to the battery bank – not the alternator. These chargers can safely pump 40 amps or more. Replace the existing cable from alternator to dc-dc charger by one of about 13.5 mm2. If the LiFePO4 is in a trailer, take the feed via an Anderson plug and socket. Then use 13.5 mm2 cable to the charger and battery. Unless done, you restrict charging current.
Lithium-ion batteries in caravans and motor homes – storage
Many advise 50% charge for storing. This, however, seems based on a report many years ago. The issue is not clear, but it is probably best to follow that until more is known. (Lithium batteries carried by air became limited to 30% charge as from April 2016.)
Lithium-ion batteries in caravans and motor homes – buying
Currently, all lithium-ion batteries are imports. Some have several levels of distribution of which each adds a profit margin. Prices for seemingly identical batteries, but different brand names, thus vary hugely.
It is still expected that lithium-ion batteries will fall in price. The Tesla release assisted – but they are not LiFePO4 chemistry or construction. A major fall is less probable as lithium sources are limited.
The essential battery management system is not necessarily supplied. Unless totally sure of what you are doing, buy only LiFePO4 batteries with the system inbuilt. Advise the vendor of exact intended usage. Obtain written assurance they are suitable for that usage. Even now (May 2017) only a few suppliers sell them.
This just (mid 2015) released lithium battery from Tesla. Pic: courtesy of Telsla Corporation (USA).
Lithium-ion batteries in caravans and motor homes – the DIY approach
Commercial LiFePO4 batteries are costly. Experimenters consequently buy far cheaper individual (3.2 volt) cells. They assemble them into packs and add battery management and energy monitoring, using proprietary and ultra-cheap components.
Not all share how to do this but some are beginning to on forums, however few know whom to trust. Unless you have experience in this area there is a risk of wrecking the cells.
Keep a sense of proportion about lithium-ion batteries in caravans and motor homes
Lithium-ion technology is a major advance. Reality, however, is that battery energy storage from 1870 to 1960. Lithium resulted in a worthwhile increase, but that really needed is many times more. Extensive research may well yet achieve this.
The most probable breakthrough is an affordable fuel cell. Such cells store energy as fossil fuel. Most such are around 12,000 Wh/kg. A LiFePO4’s is one hundred times less.
Should I use lithium-ion batteries in caravans and motor homes?
When buyers can obtain truly direct drop-in replacements, LiFePO4 batteries in RVs makes every sense. In the meantime, Caravan & Motorhome Books still advises caution. Buy only from a truly reputable vendor.
Should I use lithium-ion batteries in caravans and motor homes? – updates
This area constantly changes – so this article is accordingly updated when necessary.
Collyn Rivers’ main books in this area are the all-new Caravan & Motorhome Book, the Camper Trailer Book, Caravan & Motorhome Electrics, Solar That Really Works! and Solar Success. All cover battery charging in depth. For information about the author please Click on Bio.
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