Pic: the lithium battery co.
Lithium-ion batteries in RVs provide ample energy and power but need specialised installation to do so safely and reliably. The type generally used are the so-called LiFeP04. That term denotes their chemical make-up, i.e. is not a trade-name.
Article updated in 2019
Lithium-ion batteries in RVs – energy and power
Lithium-ion batteries in RVs have both energy and power, but for RV use that power is far greater than ever needed. Energy enables work to be done. Power is a measure of how fast that energy can be (or is) used. A child can readily stack 200 one kg cans on a shelf two metres high. An Olympic weight lifter can lift that same 200 kg overhead (two metres high) in a few seconds, Both child and weightlifter use the same total energy – but the weightlifter needs hugely more power.
Microwave ovens apart, an RV’s domestic loads need only small amounts of power. There are good reasons to use lithium-ion batteries in RVs, but their ‘power’ is not a major one. Doing so is like having an Olympics weightlifter stack shelves in a supermarket. If their weight is no issue, a 300 amp hour AGM battery bank is ample for RV loads and a fraction of their price.
Lithium-ion batteries in RVs – lighter and smaller
Lithium-ion batteries are of real value in RVs where space and weight are at a premium (as with many caravans and small motorhomes). They are about one-third of the size and weight of conventional rechargeable batteries.
Lithium-ion batteries – chargeable very fast
Lithium-ion batteries can be charged at massively high current. One of 12 volt 100 amp hour will readily accept a 300 amp charge. RV alternators usually supply up to about 70 amps during the day (with air-conditioning off) so that is a major plus. Grid-voltage chargers that size (and above) are made – but cost over $1000.
Lithium-ion batteries – almost constant voltage
In RV use, lithium-ion batteries maintain a constant 13.1-13.0 volts. This only drops to 12.9 volts when they have about 20% remaining. Maker’s advise they should not fall below that. They also claim that used like that, they are good for about 2000 such cycles. Most other batteries’ life is limited to about 500 such cycles if routinely discharged below 50%.
This graph shows the typical (per cell) voltage during discharge. That most probable for an RV is slightly above the dark blue line. That shown by the other lines are of high constant discharge and do not apply to RV use.
Such constant voltage (and in RV use) almost regardless of load, ensures that lights do not flicker when the fridge or water pump cycles on/off. Nor the fridge loses cooling, as with conventional batteries as their voltage falls.
Another lithium-ion battery plus is that energy loss whilst charging LiFePO4 is only 5% or so. That of most other types is about 20%.
Lithium-ion batteries – a truer comparison is ‘usable amp-hours’
Because of the factors outlined above, the LiFePO4 type of lithium-ion battery used in RVs must be compared on a ‘usable amp-hour basis. As a rough guide, a 100 amp-hour such battery in typical RV use has about the same usable capacity as a 130-150 amp hour AGM. They do however cost about three times an AGM’s price. For RVs with limited space and weight carrying, particularly if used for camping away from grid power, such batteries are ideal.
Lithium-ion batteries – coach conversions and large fifth-wheelers
Where space and weight capacity is less limited a 350 amp hour or so AGM battery bank will supply ample energy and power at one-third of the cost of lithium-ion. Their life-span is shorter if routinely discharged to 50% – but increasing that bank to even 450 amp hour brings it close to that claimed for lithium-ion.
Lithium-ion batteries – installation and charging
This was initially a major issue. Until recent years expertise was rare, but most auto-electricians now know how it must be done. A few LiFePO4 vendors claim they have ‘drop-in’ direct replacements (regardless of previous battery type) but then qualify that in the small print.
Further, a few LiFePO4 vendors claim ‘normal’ alternator charging is fine. This cannot be. There has been no such thing as a ‘normal alternator since 2000. Then, alternator outputs began to vary – from 12.7 volts to plus 14.7 volts. Many had voltage varying with load and/or temperature. Some now vary from plus 15 volts to 12.3 volts. Or, at times, even none.
Many major alternator chargers makers have units specifically for LiFePO4, or with a LiFePO4 option. Such chargers include under/over voltage protection and cell balancing. Some also accept solar input.
Lithium-ion batteries – pricing
This is still an issue. Unlike AGM batteries (where value equates largely to their lead content and hence weight) and have many makers, their are fewer lithium-ion battery makers. Many are the same product but sold under various brand names with equally varying supply chains – each adding its profit margin. As a result (apart from the promotion and stick-on label) otherwise 100% identical product may vary in price. This issue is lessening as competition increases – but it still cannot be assumed that high price equals higher quality.
Installing lithium-ion batteries in RVs
Apart from advising to locate the charger close to the battery bank (not the alternator), installing lithium-ion batteries and/or alternator chargers is far too complex to explain in article form. It is, however, totally covered in our associated books Caravan & Motorhome Electrics, and also Solar That Really Works! They are now in a choice of digital and print versions.
This area constantly changes – so this article (and our associated books are updated when necessary.