The lowdown on leisure batteries - is lithium right for your motorhome?
Words by Clive Mott
A leisure battery keeps all modern motorhome systems running. Even if you have a gas fridge, its electronics run from the leisure battery. So do the heating, cooking and hot water systems. Even flushing the loo requires volts!
The National Caravan Council (NCC) has a scheme that has looked at verifiable test data for a range of batteries. Class A batteries have the most capacity and largest life cycle figures. Look for the NCC Class A label on the battery.
The type of battery you need depends on your camping lifestyle.
If you only stay at campsites with hook-up then most standard leisure batteries will satisfy your needs, as they only need to power your systems when you stop for a cuppa en route. Some CLs and temporary sites have low-power hook-ups, typically 6A, so don’t try and run the electric kettle and toaster at the same time. However, most campsites in the UK offer a 16A hook-up.
Then you have those motorhomers who regularly stop for a night en route to their chosen campsite, yet still want all the home comforts, including such things as a microwave powered by an inverter. These inverters generate a ‘mains’ AC voltage and the more-expensive pure sine wave variants also match the shape of the mains voltage. The cheaper quasi-sine wave units may work with all equipment, so check before buying.
Typically inverters are used for powering phone and laptop chargers, where a 150W unit should be sufficient. If you’re charging electric bikes then look at a 600W inverter. If you want a microwave, you will need to use an inverter of around 1,500W to power it, which will use 125A so you’ll need beefy cabling to handle this. Even a 600W (output) microwave will still take nearly 90A from a leisure battery via the inverter. If this is your lifestyle then probably two 100Ah batteries will be required to support such an inverter and microwave combination, even if you’re only using it to warm pasties!
Moving up from this scenario are those motorhomers who wild camp a little more often. They need to consider how much battery energy they require and how much they can carry. To quantify how much energy, or how many amps, is needed, one first needs to convert all the outputs into amps, as we quantify batteries in ampere hours (Ah). To do this, you must divide the wattage figure by the voltage (12V in this case). Once you have this figure you can start to consider batteries.
Quality deep-cycle batteries would be best. Lead acid batteries have a finite cycle life and these are best protected by not draining them down to more than half of their total stored ampere hours. Life cycle figures are given for this 50% depth of discharge figure (DOD). So, in reality, a 100Ah battery should be considered to be only a 50Ah battery. Lead acid batteries are made to a price and the cheaper batteries will have a shorter service life and less life cycles.
The final scenario is the frequent wild camper. To keep going in this scenario you need a reliable source of power, of which solar panels are ideal.
Solar panels are silent in operation, so fit the biggest you can. Make sure you have the appropriate MPPT (maximum power point tracking) solar regulator to maximise the panel’s output and match the battery technology and, if required, a regulator that can charge both leisure and starter batteries.
It’s also worth considering a battery-to-battery (B2B) charger, which takes power from the starter battery when the engine is running to charge the leisure battery faster than a conventional split charge relay.
If your motorhome has an ‘intelligent alternator’ that converts braking energy into electrical energy to fast charge the starter battery then your motorhome may have a B2B unit already installed.
These are tailored to suit different types of battery, so choose wisely if you see one of these as a method of quickly recharging your leisure battery during 60 minutes of engine running.
When considering batteries, be aware of devices that take lots of amps:
Diesel heaters – Any diesel heating system, water or space, has a pump to squirt diesel through a small jet to make a mist and a glow plug to light this mist. Glow plugs can take 20A for several seconds each time the heater is started and this happens frequently because of the thermostat. The diesel pump and a fan are also running all the time the heater is burning and consuming from 1A to 3A.
Compressor fridges – These are more efficient than a three-way gas fridge but take a lot of power from your leisure battery, typically 5A when running under thermostatic control. So they work out at around an average of 2A if you don’t want too much cold beer. If you simply multiply the amps taken by the hours running you have the ampere hours consumed. This is 24 (hours) x 2 (A) = 48Ah a day. Top-loading compressor fridges are the best of this bunch.
Lighting is no longer power-hungry and LED lighting is by far the most economical. A 2W LED lamp (taking only 0.17A) will provide similar illumination to a 20W quartz halogen bulb. By comparison that 20W halogen bulb would take 1.7A – 10 times as much current.
For heating systems, you need to be looking at gas-powered units. Remember, a 6kg gas bottle contains as much energy as over 60 fully charged 100Ah batteries, so it can be better to use gas for anything that requires heat.
A Whale heating system takes about 1.7A when running and 0.01A on standby. The Truma Combi has similar electrical requirements when used for space heating. Both have a gas solenoid to energise them and a fan to blow the air.
The Alde wet system is more economical, requiring 0.4A for water heating only and 0.6A for hot water and space heating.
If your camping lifestyle cannot quite be supported by one leisure battery, then adding another matching battery is the best way to double your independence. Make sure that each leisure battery has its own in-line fuse for safety.
Not all motorhomes require the same type of battery. Motorhomes from Swift and Auto-Trail have a Sargent electrical system and these are best served with a wet lead acid battery, which is suitable for the vehicle charging regime.
Modern Hymer motorhomes are different, with Schaudt electrics with a different charging regime, and come from the factory fitted with AGM batteries. If you want to change the battery type, then check the manual.
Other charging systems include wind generators and fuel cell systems, such as the Efoy range that run from methanol and trickle charge batteries. Fuel cells make no more noise than a laptop computer.
The lowdown on lithium batteries
Over the past few years a new breed of batteries has arrived that is driving electric cars and is now filtering into the leisure vehicle battery market. These offer more capacity, less weight and a longer life.
Motorhomers will come across two types of lithium battery, both have a much better life expectancy compared to traditional lead-based batteries in the order of 10 times.
One type is lithium ion, which is used in devices such as phones and tablets, as well as electric bikes as it offers high amounts of energy storage for minimal weight. Like all batteries, each is a collection of serially connected cells so that the output is the addition of each cell voltage.
Most phones or tablets use one lithium ion cell and this voltage will typically be between 3.6V and 4.2V when fully charged.
Many ebikes have 10 cells serially connected and operate between 36V and 42V. Frequently these use several sets of 10 cells connected in parallel to increase capacity.
A problem comes with this cell type when one wants to replace a nominally 12V lead acid battery with lithium; the operating voltage of the cells spanning 14.4V to 16.8V is too high if you use four cells, or too low if you use three cells (giving a voltage of 10.8V to 12.6V).
The other type of lithium cell construction uses the metal iron in its chemistry, lithium iron ferro phosphate being the name and LiFePO4 the shortened version. So we have lithium ion and now also lithium iron! To minimise confusion, let’s call these iron variants lithium ferrous.
Four lithium ferrous cells have a typical end of charge voltage of 14.6V, give or take a small tolerance (0.1V or 0.2V). This is very close to the voltage required for lead acid batteries.
Several sources suggest the use of dedicated lithium charging systems that simply switch off at 14.6V and on again at a much lower voltage, while many say that the LiFePO4 battery can be used as a direct replacement for a lead acid battery.
Other advantages provided by lithium ferrous batteries are intrinsic safety (compared to lithium ion which have been known to catch fire), the ability to discharge regularly to 90% without seriously compromising the battery life and lower weight.
If you factor in the general advice not to discharge a lead acid battery below 50%, then a 50Ah lithium ferrous battery can provide the same amount of useable energy as a nominal 100Ah lead acid battery.
I have replaced three 95Ah AGM lead acid batteries with one early-generation 150Ah lithium ferrous battery, which has saved us 61kg. This weight saving was the fundamental reason for changing.
All lithium ferrous batteries consist of many cells connected in both series and parallel. Several cells are connected in parallel to provide the required ampere-hours, and four sets of parallel-connected cells are then connected in series to provide the required output voltage.
Individual cell construction is either cylindrical or prismatic. Prismatic cells nest together better as the shapes fit together, cylindrical cells laying alongside each other waste more space but are said to have a better cycle life.
Charging lithium batteries
Lithium ion and lithium ferrous batteries can accept large amounts of charge current and provide large discharge currents; however, this technology is fragile in that it can be damaged by gross overcharge or gross overdischarge. To protect against this, inside each battery there is a battery management system (BMS) that monitors the voltage of every cell and will switch off the battery if the set voltage limits are reached for any cell.
If you run a hair dryer or even a microwave via an inverter then you need a battery with a BMS of around 150A. A 50A BMS will be insufficient.
A lead acid battery does not have a BMS. Another difference is the working temperature range for lithium ferrous batteries. The range for discharge is typically -10˚C up to 60˚C. The range for charging is more limiting, being typically between 0˚C up to 40˚C.
Don’t try to charge a lithium ferrous battery if it has been left in a sub-zero environment for a while as you can do permanent damage if the BMS does not provide temperature protection.
The advice is to mount lithium ferrous batteries inside the living area of a motorhome to keep them safe.
Starting up a motorhome with a fast B2B leisure battery charging system that has been stood empty overnight in sub-zero temperatures can lead to rapid damage if protection is not built in.
Not all BMS systems are the same. Some provide cold protection, while others do not.
Lithium ferrous cost
Currently, prices are about £10 per ampere hour for most, but competition and increasing popularity means that prices are coming down.
Many lithium ferrous batteries are supplied with an external display panel where their operation can be monitored, including percentage of capacity remaining, charge current and voltage. Some batteries include bluetooth and are supported by a phone or tablet app.
Lavi offers a premium package including a built-in B2B fast charger and solar regulator all in one box. A few have grasped the nettle regarding sub-zero charging and have heaters inside the battery that use the charging energy to power the heaters initially until the battery has got up to working temperature.
Hymer has partnered with Bos to create a Lego-type battery arrangement. The Hymer 135Ah lithium ferrous battery is a sandwich of six Bos LE300 12V units put together as one block. Hymer has downrated the 153Ah battery to 135Ah to prolong cycle life and offers three variants using lithium ferrous and lead batteries alongside each other so that the high currents come from the lead-based batteries, which also accept a charge in sub-zero temperatures. The lithium batteries also include heaters.
Warranty for lithium ferrous batteries
Even if fully charged and discharged every day, the warranty in most cases would expire well before a typical user had reached the published cycle life of a lithium ferrous battery.
Transporter Energy offers the best warranty of 10 years with its 100Ah battery and the internal BMS protects the battery should the temperature become excessively high or low, stopping charging at -4˚C.
If your priority is maximum capacity, fast charging and discharging and minimum weight and space then you need to look seriously at lithium ferrous batteries.
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