Updated 28 September 2016
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, and for lightening overweight RVs. All can supply high peak power. They can also be used as deep cycle batteries. Their chemistry and working is very different from traditional batteries: they are almost a different species.
Since the last major update, it has become apparent that whilst technically minded people understand what is meant by power, ongoing promotion (stressing a lithium battery’s far greater power) is causing many to confuse that with far greater energy. This is causing many (including the odd vendor) to quite wrongly believe that lithium ion batteries store more energy than conventional batteries of similar capacity. This is absolutely not so.
Energy and power are not the same
Energy is that property that enables work to be done – in this case electrically. Power relates only to how fast that energy is used. A really good example is a car’s starter motor. The energy needed is a truly small amount. It’s about that needed to run a 5 watt LED for an hour. But those 5 watts is used in only a second or two – and that’s a lot of power. The lead acid starter batteries still used are designed accordingly.
The deep cycle batteries used to power the electrics in camper trailers, caravans and motor homes cannot rival a lithium ion’s ability to power really big loads, but this is not necessarily an issue for those able to carry a (about) 12 volt 300 amp hour battery bank – particularly if gel cell or AGM. One’s that size do not remotely rival a LiFePO4’s ability to supply massive power – but that is of no value unless such power is needed. Not realising this can result in your being sold very costly batteries that you do not require.
Lithium-ion battery types
Lithium cobalt oxide (LiCoO2) batteries store the most energy – a bonus for aircraft makers. In January 2013 however, one of them started a fire in a Boeing 787. United Airlines reported two more such fires a day or two later. All Boeing 787s were grounded for a time. These fires made headline news, but the lithium-ion batteries (LiFePO4) in caravans have very different chemistry.
This LiFePO4 battery is claimed to be able to be charged by most good quality two-stage battery chargers – the battery management system (see below) is inbuilt.
The lithium-ion batteries (LiFePO4) in caravans and motor homes are less energy efficient than LiCoO2 batteries. They can ignite but the graphite (used for one electrode) must reach over 10000 C to do so. In effect they are close to non-flammable. At approximately 105 watt hours per kilogram they are about third the size and weight of lead acid batteries of similar rated capacity. They are claimed to be non-toxic but waste recovery experts stated (at a 2016 IDC Conference) that they are posing major 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 is not applicable to general caravan and motor home use.)
Unlike a lead acid battery’s 12.8-11.4 volts, lithium-ion batteries in RVs (LiFePO4) voltage output remains almost constant. For lithium-ion batteries in caravans and motor home use it is likely to remain at 13.1-12.9 volts once below 90% or so full charge. This is a major plus as voltage drop issues are minimised. Voltage falls off steeply at 10% or so remaining. Lithium-ion batteries are damaged or their life shortened (some claim they are ruined) if fully discharged. Such discharge must be limited by an obligatory battery management system.
This close to constant voltage output of lithium-ion batteries in caravans virtually eliminates low voltage fridge issues, and halogen lights dimming. Lithium-ion batteries in caravans and motor homes also benefit owners who free camp and have the lack of battery capacity issues associated with 230/12 volt converters. See Electrical Converter Problems in RVs-update.
Batteries differ in their ability to supply high current loads at a usable voltage over time. Here, deep cycle lead acid batteries are very limited, gel cells and AGMs are better and lithium-ion excels. A LiFePO4 18 Ah jump starter safely and reliably supplies starter battery level current for a short time but can serve also as a short term deep cycle battery.
Lithium-ion battery safety
LiFePO4 and similar batteries are able to release massively high current. Extreme care is necessary to never accidentally short circuit their terminals. If done, the instantaneous current flow can instantly vapourise whatever does it. If that were a spanner it would not be good to be holding it at the time. Always wear safety glasses and protective clothing when working on or near any battery.
Install circuit breakers as close to the battery as possible. These should rated at the safe current the cabling to appliances etc can carry. This will safeguard cables from catching fire, or melting in the event of a short circuit across them.
Lithium-ion batteries do not vent gas unless charged/discharged at more than triple their amp hour capacity. Venting may occur above that. Their makers claim the emissions are neither toxic nor explosive. Ventilation is nevertheless advised to limit heat build up.
Whilst this varies from maker to maker, LiFePO4 batteries have a preferred working range of -18 degrees C to about + 40 degrees C.
Cell monitoring is essential
The upper safety limit for a LiFePo4 cell is generally agreed to be 4.2 volts. If however, for any number of reasons (aging, excess charging voltage, etc,) a 12 volt LiFePO4 battery (charging at 14.4 volts) were to have three cells at a safe 3.2 volts the remaining one will have 4.8 volts across it. That cell will heat up and may ignite or even explode.
It is claimed that an overly discharged LiFePO4 can sometimes be brought back to life by initially recharging at very low voltage and current. This needs bringing each cell to an initial 3.2 volt. It requires a specialised charger.
Another risk is that there may be a cell so unbalanced that ongoing discharge could cause remaining cells to reverse that unbalanced cell’s polarity. Any subsequent attempt to recharge (warns EV Australia) ‘carries a significant risk of catastrophic failure’.
To prevent the above, a cell management system must be used. This system can be within the battery housing, or external. Control of charging and discharging voltage and current too is essential. This may be included within that battery management system, or the battery charger’s. Reputable suppliers warn that LiFePO4 cell management is essential – but it is not necessarily routinely supplied.
The more cells that are series-connected, the greater the risk of unbalance. As a generalisation, the larger the individual 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.
Many LiFePO4 users have strong views about the charging routine. These extend (in my experience) even to objecting to reporting disparate manufacturers’ information. This article simply reports there are two main approaches. That recommended by some LiFePO4 battery and battery charger makers, and that of many ‘do it yourself’ users. All regard cell management as vital. Most agree that discharge be limited to about 10% remaining charge. The main area of contention relates to the final state of charge, i.e, how close to 100% is safe.
This graph shows the relationship between charging voltage, current and a typical LiFePO4’s state of charge.
A 12 volt lithium-ion LiFePO4 battery is commonly accepted to charge safely to 80%-85% at a constant 13.6 or so volts. Many DIY users (including the author for a now five years) do just that. If discharge is curtailed at 10%, usable capacity is 70%-75%. Much of the LiFePO4 industry however (in effect) argue that charging deeper enables you to utilise more of the paid for capacity.
So why not (they say) do so? A common industry approach is thus to charge at constant current to about 90% full. A few LiFePO4 charger makers then apply a tightly controlled fixed voltage of a typical 14.6–14.65 volts. This requires very accurate control (95% charge is about 14.4 volts). It is surprisingly hard to measure such voltage (and current is harder) accurately and consistently – let alone control it.
In terms of charging efficiency, LiFePO4 is way ahead. Vendors claim 92.5-95% and that is probably true: that of lead acid batteries is about 80%.
Lithium-ion battery lifespan
The battery industry’s usual way of defining a battery’s useful life is the number of charges/discharges that can be drawn before capacity falls to 80% of that when new. With lead acid deep cycle batteries this is very much related to ongoing depth of discharge etc. Some users and vendors claim that a LiFePO4 (in RV usage) is barely affected by the rate of discharge. LiFePO4 batteries are typically drawn down to 20% or less remaining charge but doing so is now being claimed by some to limit battery lifespan.
Most claim about 2000 cycles if discharged to 20% remaining (virtually regardless of load). Some suggest this can be extended by limiting the maximum charge to 90%. Not all LiFePO4 battery chargers, however, have settings which enable that.
In all of the above it needs to be remembered that LiFePO4 batteries only began to be used on a largish scale around 2012. All claims re their lifespan are thus based on a mix of accelerated cycling and speculation. There can be no proven real-life data until until 2022 or so.
Lithium-ion mains battery chargers
Some lithium-ion battery makers advise that, providing battery monitoring and charging control is in place all that required is a two-stage charger. Many users disagree. It is however becoming generally agreed that using an intelligent LiFePO4 charger is safer than using a standard lead-acid battery charger.
Alternator and/or solar charging
It is commonly claimed (for LiFePO4 charging), that ‘normal alternator charging’ is fine. That cannot be. There has been no such thing as a ‘normal alternator since 2000. About then, alternator outputs began to vary, from 12.7 volts to plus 14.7 volts. Some have voltage that varies with load and/or temperature, and some have voltage that varies from plus 15 to 12.3 volts (or even none at all at times).
Companies such as Redarc and Sterling produce alternator chargers specifically for lithium-ion LiFePO4 (or with a LiFePO4 optional regime). They stress that their units must only be used with lithium-ion LiFePO4 batteries tested and approved by Redarc. These systems must include under/over voltage protection, cell balancing, and able to handle the charge current. Some also accept solar input.
The (Australian designed and made) Redarc LFP 1240 alternator charges a LiFePO4 12 volt battery at 40 amps – it also accepts input from solar modules. Pic: Redarc.
For charging lithium-ion batteries in caravans and motor homes a LiFePO4 dc-dc alternator chargers should be located as close as feasible to the battery bank (i.e. not the alternator). These chargers can safely 40 amps or more into a LiFePO4 battery bank. It thus helps immensely to replace the existing cable from the alternator to that dc-dc charger by one of approximately 13.5 square mm. If the LiFePO4 is in a trailer, take the feed via an Anderson plug and socket, then 13.5 square mm cable to the charger and battery. Unless that is done, the charging current will be unnecessarily restricted.
Lithium-ion battery storage
Like much about lithium-ion batteries in caravans and motor homes, this area too is contentious. As of April 2016 lithium batteries carried by air are now limited to 30% charge Many claim that 50% of charge is also best for storage but this seems based on just one report/recommendation of many years ago. The University of Texas however stated that storing a fully charged battery has minimal impact on its life span. The issue is not clear, but it seems best to follow that 50% until agreement is reached.
The essential battery management system is not necessarily supplied with all LiFePO4 batteries. Unless you are totally sure of what you are doing it is strongly advised to buy only LiFePO4 batteries with the system inbuilt, to advise the vendor of the exact intended usage, and to obtain written assurance that they are suitable for that usage. Right now (June 2016) there are only a few reliable suppliers of these batteries. They are not stocked by most battery vendors.
A few LiFePO4 batteries are promoted as drop-in replacements for existing lead acid batteries. This claim is hard to take seriously as many post 2013 alternators generate over 15 volts – some as high as 15.4 volts in vehicles with regenerative braking (enough to destroy a 12 volt LiFePO4). See http://caravanandmotorhomebooks.com/smart-alternator-problems-with-rvs/.
Lithium-ion battery pricing
Currently, no lithium-ion batteries are manufactured in Australia. All are imported. Some have several levels of distribution. Each adds a profit margin. Prices for often seemingly identical batteries sold under different brand names range from A$1000 to A$3000. Some are claimed to be rebadged versions that can be bought otherwise cheaper. It is not however an area for eBay specials unless one is certain of what one is doing. Lithium-ion batteries were originally expected to fall in price as they become increasingly accepted. The recent US Tesla release assisted this – but they are not of the LiFePO4 chemistry or construction (they are a vast number – each of only 15 Ah). This long term fall in price is no longer seen as probable because the world’s lithium sources are limited.
This just (mid 2015) released lithium battery from Tesla. Pic: courtesy of Telsla Corporation (USA).
Lithium-ion batteries in caravans and motor homes – buying
Unless you are totally sure of what you are doing it is strongly advised to buy only LiFePO4 batteries with the system inbuilt, to advise the vendor of the exact intended usage, and to obtain written assurance that they are suitable for that usage. Right now (September 2016) there are only a few reliable suppliers of these batteries. They are not stocked by most battery vendors.
A few LiFePO4 batteries are promoted as drop-in replacements for existing lead acid batteries. As noted earlier in this article this claim is hard to take seriously as many post 2013 alternators generate over 15 volts – some as high as 15.4 volts in vehicles with regenerative braking (enough to destroy a 12 volt LiFePO4). See http://caravanandmotorhomebooks.com/smart-alternator-problems-with-rvs/.
The DIY approach
LiFePO4 batteries are costly if bought from commercial suppliers. Experimenters can save over 50% by buying individual 3.2 volt cells, assembling them into packs and adding a battery management system plus energy monitoring. A number of electrically knowledgeable experimenters have also devised advanced ways of achieving the above using proprietary ultra-cheap monitoring systems.
Some prefer not to share this openly. Others are now beginning to do so openly on Internet forums but in hi-tech terms. Even if explained simply it is impossible for most readers to know who to trust. Unless truly knowledgeable and experienced in this area there is a very real risk of wrecking a LiFePO4 battery by such experimenting. It is for this reason that Caravan and Motorhome Books and Successful Solar Books advise to obtain reliable technical advice prior to purchasing.
Keeping a sense of proportion about lithium-ion batteries in caravans and motor homes
Lithium-ion technology is a major advance in terms of weight and volume. The reality however is that battery energy storage has otherwise barely increased since 1870. The advent of lithium-ion has resulted in a worthwhile increase. But that really needed is 10-20 times more. Extensive research may well achieve that.
The most probable breakthrough is an affordable fuel cell – where the stored energy stored is its fossil fuel. Most such fuels are around 12,000 Wh/kg. That of energy stored in a LiFePO4 is one hundred times less.
Should I use lithium-ion batteries in caravans and motor homes?
As any forum involved in lithium-ion batteries in caravans and motor homes shows, this is still a hugely contentious area. Some users (but not all vendors) have an almost religious belief in a LIFePO’s attributes – perceived or otherwise. As one major lithium-ion battery vendor emphasises, if size and weight is not an issue, most caravan and motor home 12/24 volt electrical needs can be readily handled by a 300 amp hour (upwards) bank of AGM batteries at well under half the price – and next to no complication. Caravan & Motorhome Books by and large agrees with that vendor. But where weight carrying and space is limited the smaller and lighter LiFePO4 approach makes sense (albeit it at considerable price).
A major problem still affecting lithium-ion batteries in caravans and motor homes is that few battery vendors sell LiFePO4 product. Expertise is scarce. Several vendors claiming such disagree openly and often strongly on Internet forums. There are a few (mostly small) companies that know their stuff. Non-technical prospective buyers, however, have no way of telling which is which.
If and when these issues are resolved, prices fall, and non-technical buyers can obtain a truly direct drop-in replacement for what they have now, using lithium-ion batteries in caravans and motor homes makes sense. Until these issues are resolved (or one buys only from a vendor that truly understands that required), Caravan & Motorhome Books still advises caution in using lithium-ion batteries in caravans and motor homes.
It helps if you have a good technical background and understanding of this technology. Or know someone who truly does. Or locate a company with proven lithium-ion expertise (there are some).
As this area is constantly changing this article will be updated every few months, or sooner if deemed warranted.
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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