CAMPING - POWER & LIGHTING
Back in the good old days you could have any battery you liked, so long as it was black, heavy and full of easily-spilled acid. Now, there’s a choice of several different types.
Lead acid batteries, be they the traditional ‘flooded’ type, or no-maintenance, valve-regulated lead acid (VRLA) – so-called ‘starved-electrolyte’ gel and absorbed glass mat types – store energy in a reversible electrochemical reaction that takes place between lead and lead dioxide plates and sulphuric acid
In theory, the discharge and recharge action should go on indefinitely, but the chemical world isn’t perfect: some salts fall out of suspension and build up on the bottom of the casing; some energy is lost to heat; a small amount of lead is lost to electrolytic action; and hydrolysed water (hydrogen and oxygen gases) is produced.
Another issue is ‘settling’ or stratification of the electrolyte in flooded batteries that aren’t shaken about very much, reducing the efficiency of the chemical reaction.
Of all battery inefficiencies, electrolyte ‘stratification’ and hydrogen and oxygen (water) loss have proved to be the easiest to improve.
The traditional flooded, wet-cell battery is the lowest-priced option, but it suffers from the aforementioned stratification and water-loss issues.
Stratification of the electrolyte needs to be countered by ‘equalising’ or ‘boost charging’ a flooded battery periodically. In this operation the slight overcharge results in oxygen and hydrogen bubbles being produced at the plates and this action ‘stirs’ the electrolyte.
The method of water loss replacement in a traditional ‘flooded’ battery is quite familiar: periodically remove the caps and top up the cells with distilled water.
However, both these operations are often neglected or wrongly done, shortening battery life.
Valve-regulated lead acid (VRLA) batteries were developed to overcome water-loss and stratification problems.
Although called ‘sealed’ batteries, VRLA types do have a relief valve, to prevent an explosive gas build-up in cases of extreme overcharging. However, in normal discharge and charge operation the VRLA battery does not vent to atmosphere.
The hydrogen and oxygen gases produced at the plates are retained inside the casing and ‘recombined’ using an internal catalyst, so there is no water loss.
Often marketed as low- or no-maintenance batteries is a crop of cheaper, semi-sealed, flooded batteries that are not true VRLA types. These modified starting batteries have reserve electrolyte storage, but once that’s used up, are finished.
This VRLA battery has its electrolyte thickened to a jelly state, which prevents stratification. Another plus is that a gel battery case fracture results in an oozing of electrolyte, rather than a flood of acid.
Gel batteries can be left in a discharged state for a long period of time and still recover. However, gel batteries require lower-voltage charging than flooded batteries and most gel batteries should never be equalised.
In a gel battery that is being incorrectly overcharged, gas bubbles cause voids that increase resistance and can cause damage through heat build-up.
The gel battery manufacturer’s charging recommendations must be followed to the letter.
Absorbed Glass Mat batteries
The AGM VRLA battery type has its acid suspended in a glass-fibre mat, which overcomes electrolyte stratification and leakage problems.
Like any VRLA battery, an AGM battery should not be overcharged. Some high-quality AGM batteries can be equalised, but only under controlled, constant current conditions.
Manufacturer recommendations for correct charging must be followed closely.
AGM batteries don’t like heat and won’t be warranted in an under-bonnet location unless the casing is a special heat-insulated type.
Lead crystal batteries
This VRLA battery type is relatively new in Australia, but the technology has been around for many years. Lead crystal technology was patented under United States Patent 4143216 in 1979:
‘A unique storage cell is provided in which the active mass on the positive electrode is a mixture of crystalline and an effective amount of polycrystaline lead super-oxide (PbO2).
‘These cells are characterised by their remarkably
lower internal resistance, higher activity, better charging and discharging characteristics, lower sulphatisation, higher storage capacity and greater ability to draw larger amounts of electric current in a considerably shorter period of time as compared with conventional lead-acid storage cells.
‘A battery made from such cells also exhibits superior performance characteristics as compared with storage devices made from conventional lead-acid cells. Batteries made from such cells will be referred to as ‘lead-crystal’ batteries.’
Note that the comparison is with flooded lead acid batteries, not more advanced AGM or Gel types, let alone lithium ferro-phosphate batteries. The only lead crystal battery maker claims it has better discharge tolerance and faster recharge time than Gel or AGM.
Lead crystal batteries are said to tolerate deep discharge better than other types and are also said to have more cycling life. However, while they can withstand deep discharge and partial charging they do need periodic mains charging at the correct current rate, to maintain battery life.
Betta Batteries warrants its lead crystal battery in under-bonnet locations, unlike AGM or Gel battery makers, however, the small print is worth reading:
‘When the ambient temperature is at a constant 40°C the battery cycle life decreases with 23%. Every 10°C additional increase in temperature, means an additional 13% reduction in cycle life”.
Under-bonnet temperatures regularly exceed 60C, so at OTA we wouldn’t recommend under-bonnet fitment.
Everyone these days is familiar with the rechargeable lithium-ion battery that powers most mobile devices, from phones to power drills, so it seems strange that it’s taken so long for battery makers to produce a reliable, automotive deep-cycle lithium battery.
The principal issues that have delayed the lithium deep-cycle battery are safety improvements and development of a specific charging system. Well-publicised fires in aircraft using lithium-ion batteries had to be avoided.
Where the familiar rechargeable appliance lithium-ion battery is a lithium-cobalt type (LiCoO2) the automotive deep-cycle version uses lithium iron phosphate (LiFePO4) technology.
This LFP battery (Lithium Ferro-Phosphate) uses LiFePO4 as a cathode material, because it’s a more stable compound that resists breakdown much better than LiCoO2 if short-circuited or overheated. The LFP battery won’t catch fire in the way an LCoO can and also offers longer life, a better power delivery rate and a constant discharge voltage.
The downside is heavier weight than an LCoO, but both types weigh only around one-third of lead-acid batteries.
Also, where a lead-acid, gel or AGM battery should not be discharged below around 70-percent of its amp-hour capacity the LFP battery is said to be fine with discharge as low as 20 percent. That allows the LFP battery to deliver more than twice the power of a traditional battery, from around one-third the weight.
On top of that, the LFP battery holds 12.8-12.5V until it reaches that 20-percent point, allowing the battery to deliver virtually full power until it is discharged, whereas a traditional battery loses voltage progressively as it discharges.
But there’s more: charge cycle life is said to be up to 10 times that of a traditional battery and charging times are typically 1.5-four hours.
We’ve been using a Revolution lithium-ion 100Ah deep cycle battery in our Tray Tek slide-on camper for the past five years, without any issues. It’s charged by a Redarc Manager30 battery management system.
Starting and Deep Cycle batteries
Flooded batteries, gel batteries and AGM batteries can be starting or deep cycle types and top-quality models of all three types can perform both functions, if they’re correctly sized for the task and maintained with the appropriate charging system.
Lithium-ion batteries are deep-cycle only.
There are also dual-purpose, flooded, gel and AGM designs that aim for the middle ground between true deep-cycle types and starting batteries.
As the name suggests, a starting battery is primarily designed to start an engine and power ancillary equipment while the engine is running and the alternator is recharging the battery.
Engine starter motors need a large starting current for a very short time, so starting batteries have a large number of thin plates, for maximum plate-to-acid surface area.
When a starting battery is discharged, some of that light plate material falls to the bottom of the casing. Repeated discharging erodes the plates to the point of failure.
Pure, deep-cycle batteries are designed to be discharged down as much as 70-80 percent throughout their lives. The deep-cycle battery’s heavy plates resist erosion, but there’s less usually surface area to deliver the cranking amps that a similar-size, dedicated starting battery can.
Lithium deep-cycle batteries can be discharged to as low as 20 percent of capacity.
How Big a Battery
Typical lead-acid battery cells are rated at 2.1 volts, so a nominal 12-volt battery has six such cells.
It’s easy enough to calculate what size battery you need and how long you can expect it to last before recharging.
Batteries are rated in ‘amp-hours’. A battery rated at 100AH will deliver 5 amperes over a 20-hour period, at room temperature.
If we assume four hours of fridge operation each day you’ll need 300 Watt-hours/day (75W x 4hrs). Two hours of fluoro light operation or about three times that of LED lighting is another 30Wh/day. Add another 30Wh/day for a couple of hours of radio operation and that totals about the minimum power consumption
a 4WD camp can expect: 360Wh/day.
On the face of it the battery capacity needed is 360 divided by 12V = 30 amp-hours (AH). However, battery makers recommend no more than 70-percent battery discharge, so to guarantee a 30AH supply a conventional battery needs to have 100AH capacity. A lithium battery can be considerably smaller.
Ampere (A) and coulomb (C) are two measurement units of electrical current flow. The current in a conductor is measured in amperes, whereas coulombs measure the amount of charge – hence the importance of C in battery design.
One ampere is equal to the flow of one coulomb of charge in a second.
In differentiating batteries, discharge current is usually expressed as a ‘C-rate’. A C-rate is a measure of the rate at which a battery is discharged, relative to its maximum capacity.
A 1C rate means that the maximum discharge current will discharge the battery in one hour. For a battery with a capacity of 100 amp-hrs, this equates to a discharge current of 100 amps. A 5C rate for this battery would be 500 amps, and a 0.5C rate would be 50 amps.
A top-quality, relatively expensive lithium ferro-phosphate battery, such as the Revolution Power 100Ah Lithium Battery, typically has a 1C cell rating, which means that 100 amps can be safely discharged from it for 60 minutes.
Many less expensive LPO 100Ah batteries have a 0.5C cell rating, which means that only 50 amps can be safely drawn from the battery for 60 minutes. In many cases, however, that C-rate is matched to a 100-amp continuous discharge battery management system, inside the battery casing.
If 100 amps is drawn continuously from a 0.5C-rated cell, the voltage drops dramatically, and the battery will be fully discharged in 30 minutes. In doing this, the cells in the battery become heavily stressed to deliver the high current and will result in reduced performance and overall battery cycle life.
This doesn’t mean that a 1C battery is inherently better for running a fridge, fan and lights than a 0.5C battery, but it does have higher discharge current capacity if required, when, for example, running an inverter.
Keeping your batteries in good condition is an important as the choice of battery type. If your camper is based at home or close to mains power it’s easy to keep the batteries charged by connecting them to a mains-supply battery charger.
Old-style 240Vchargers didn’t have the ability to charge batteries optimally, but modern electronically controlled units can be connected permanently.
If you have two different battery types, on separate circuits, they need to be charged separately, using a different charging regime for each type.
If two batteries are to be connected to a single circuit via a typical rotary isolation switch it’s important that the battery types be similar: two flooded, two AGMs or two gels. Lithium batteries need a dedicated charger and cannot be used with a conventional charger.
A modern amp/volt meter gauge will show your battery situation and remember, a ‘flat’ battery is one with an open circuit voltage of around 11.8V and a loaded voltage around 10.5V.
When on the road, don’t rely on the engine alternator current to keep a remotely-mounted battery in top condition – charging is usually spasmodic and the voltage may not be optimum.
A charging system such as the Bainbridge Technologies unit has heavy cabling and Anderson plugs at the camper trailer connection, to reduce voltage drop, feeding power to a permanently connected voltage controlled relay near the battery.
The Projecta DC20 system uses a lighter cable to deliver power to the charging unit in the trailer. The charger boosts voltage to the 14.4V, regardless of the voltage drop in the wires.
Which Battery Type for You
In the battery world, generally you get what you pay for.
The traditional flooded battery is the most popular choice, because it’s usually the cheapest and most readily available. However, within the flooded battery ranks there is a wide quality spread. If you have a good battery maintenance regime it’s worth spending on a heavy duty battery that will last four times as long a ‘cheapie’ and deliver more power in the process. Flooded batteries are priced in the $140-$300 bracket.
The next step up the quality chain is to VRLA, gel-filled or AGM, no-maintenance batteries.
No-maintenance is something of a misnomer, because regular charging greatly extends battery life, but you don’t have to top up cells. Gel batteries need a specific charging regime, via a modern, electronically controlled charger.
Lightweight, spiral-wound AGM batteries can be mounted in any position – even upside down. VRLA batteries are around the $500 mark. However, AGM batteries don’t like heat and need to be insulated if mounted in an engine bay.
Lithium batteries are around twice the price of conventional batteries, but are one-third the weight, are claimed to last much longer and can be discharged to much lower levels.
Check out the current lithium situation: