Lithium batteries for travel trailers

by Collyn Rivers

Lithium batteries for travel trailers and motorhomes 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 are very different from traditional batteries. They are almost a different species.

Energy and power are not the same

Energy enables work to be done. Power relates to how fast energy is used.

Many vendors claim a 12 volt 100 amp-hour lithium has more energy than an equivalent AGM. This cannot be. Their energy capacity is identical. Both can thus do the same amount of work. A lithium battery, however, can charge and release energy much faster.

The ability to release high power enables a small lithium battery to start a 4WD. It can do so many times. Doing necessitates high power. The energy needed, however, is tiny. It’s about that drawn by a 5 watt LED in an hour. But supplying 5 watts (at 12 volts) in the required second or two demands high power. Conventional batteries cannot match lithium’s ability to do so. An 18 Ah LiFePO4 can act as a small deep-cycle battery. It can also supply starter battery current.

Unless truly high power is needed, lithium’s ability to do so confers no benefit. If weight is no issue, a sealed lead-acid or AGM battery bank suffices for RV use. An AGM is preferable for frequent microwave oven use. Or powering a big winch.

Unless needed, high power has no value.

Pic: http://www.technomadia.com/lithium

Lithium batteries – battery types

Lithium bacobalt oxide (LiCoO2) batteries store the most energy but proved fire-prone. Lithium-iron batteries (LiFePO4) have different chemistry.

This LiFePO4 battery is claimed chargeable from two-stage battery chargers. Its battery management system (see below) is inbuilt.

LiFePO4 batteries can ignite but must exceed 1000º C to do so. They are close to fire-proof.

These batteries store about 105-watt hours/kg. This is three times more than other batteries of similar capacity. They are claimed to be non-toxic.

This graph shows the typical (per cell) voltage during discharge. That most probable for an RV is slightly above the blue line. The red line does not apply to RV use.

A LiFePO4’s voltage remains almost constant. It is typically 13.1-12.9 volts in RV use. It drops steeply at 10% or so remaining. The batteries’ almost constant voltage eliminates low voltage issues.

Battery management in travel trailers and motorhomes

LiFePO4s suffer damage or ruin if fully discharged. Over-discharge must be limited. Furthermore, the upper safety limit of a LiFePO4 cell is 4.2 volts. If exceeded that cell heats up. It may ignite or even explode. Another risk is of cells reversing polarity. Controlling charging and discharging voltage and current is essential. This is done by a management system. Or the battery charger.

The battery management system essential for lithium batteries is not necessarily supplied. Unless of what you are doing, buy only those with the system inbuilt. Advise the vendor of the intended use. Obtain written assurance of suitability for that use.

Such chargers include under/over-voltage protection, cell balancing and solar input.

LiFePO4 cell management is essential. It is nevertheless not always supplied.

Safety

LiFePO4s release massive current. Never short-circuit them. Wear safety glasses and protective clothing when working on batteries. It is essential with lithium.

Install circuit breakers close to the battery. Rate these for the current your may carry. This safeguards against burning if cabling is overloaded.

Unless charged/discharged at massive levels, lithium batteries rarely vent gas. Vendors claim emissions are neither toxic nor explosive. Nevertheless, ventilate to limit heat build-up. Most have a recommended working range of -18 degrees to + 40 degrees C. They are damaged by exceeding 40 degrees C.

Charging & monitoring

Not all LiFePO4 users agree about charging. Most advise limiting discharge to about 10% remaining. Some advise not to fully charge. That charging to 90% is safer. They do so at about 13.6 volts. Many DIY users do  If discharged to 10%, usable capacity is 70%-75%. Deeper charging provides close to full capacity. Doing so, however, requires accurate control.

LiFePO4’s charging efficiency excels. Vendor claims of 92.5-95% seem realistic. Lead-acid’s is about 80%. of AGM’s is about 85%.

This graph shows the relationship between charging voltage, current and LiFePO4 state of charge.

Usable lifespan

Their makers regard battery termination when capacity is 80% of new. Conventional battery life is shortened by ongoing deep discharges. LiFePO4 lifespan is virtually unaffected. Vendors claim 2000 cycles if discharged to 20% remaining. And by more limiting charging to 90%. Not all chargers enable this.

Extensive LiFePO4 usage began in 2012.  Claimed lifespan is based on speeded-up cycling. There can be no real-life data until 2022. Anecdotal evidence indicates it is probably 8-10 years.

Charging

Some vendors advise using a two-stage charger. Many users disagree. They claim dedicated chargers are safer. Also claimed is ‘normal alternator charging’ is fine. This cannot be. There have been no ‘normal’ alternators since 2000. Most alternator outputs vary from 12.7 volts-14.7 volts. Some vary from plus 15-volts – 12.3 volts. Or even zero.

Many makers produce specifically LiFePO4 alternator chargers. Some provide general chargers with a LiFePO4 option.

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 close to the alternator.

These chargers may supply 40 amps or more. Replace existing charging cables by those of about 13.5 mm². If the battery is in a trailer, take the feed via an Anderson plug and socket. Use 13.5 mm² cables to the charger and battery. Unless done, you restrict charging current.

Storage

The still common advice to use a 50% charge for storing stems from a report many years ago. Most makers now advise 40% charge and to store in a cool place.

Lithium batteries for travel trailers and motorhomes – buying

Currently, all lithium-ion batteries are imports. Some have several levels of distribution. Each adds a profit margin. Prices for identical batteries (but with different brand names) vary hugely. It pays to shop around.

Lithium batteries may fall in price but a major fall is improbable. This is because lithium sources are limited.

Lithium batteries – the DIY approach

Commercial LiFePO4 batteries are costly. Experimenters cheaper individual (3.2 volts) cells. They assemble them into packs. They then add battery management. Also energy monitoring. Don’t attempt this unless you experienced. There is a risk of wrecking cells.

Keep a sense of proportion about lithium batteries

Lithium technology is a major advance. Battery energy storage from 1870 to 1970, however, barely changed. Lithium is a worthwhile increase. That really needed, however, is far more. Extensive research shows this to be feasible.

The most probable breakthrough is cheaper fuel cells. Such cells already store are around 12,000 Wh/kg. A LiFePO4’s is one hundred times less.

Should I use lithium batteries in travel trailers and motorhomes?

When buyers can obtain truly direct drop-in replacements, LiFePO4 batteries in RVs makes every sense. In the meantime, RV Books advises caution. Buy only from a truly reputable vendor.

Should I use lithium batteries in travel trailers and motorhomes? – updates

See also: https://rvbooks.com.au/lifepo4-jump-starters-really-do-work-2/

Collyn Rivers’ main books in this area are the 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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