Updated : 01/06/2017 

"Allan, I ordered 2 new batteries, installed today and what I thought was a faulty Reich e-Box is now working well. You were right, battery condition is everything.

Thank you so much.


Some people want to understand how a battery works so they can make an informed purchase and give it the ideal care to prolong it's life. Often after experiencing a failed battery. 

One of the most common questions they want answered is why did their battery fail? So we will start at the other end and cover why batteries fail and the most common causes, then gradually make our way back to how they work. 

                                  'What makes a Lead Acid Battery Fail'


For much of this section we are going to primarily rely on Andrew Goodwin's lifetime work, a document  'Battery - Lifetime Study' published in 2014. 

The full document can be found further down the page, should you wish to read it in it's entirety, but we are going to Cherry pick some of the findings, some of which go against the generally held views in the Motorhome community.

The study was primarily of Lead Acid batteries used in battery backup systems that are generally lightly used and kept at full capacity by a permanent 'trickle/float' charge, just as many Motorhome batteries are kept 'charged up' by long term connection to a Mains Supply or a Solar Panel. Therefore the study has more relevance to Motorhomes than might be first thought. Far more relevant than the usual comparisons made with Car Starter batteries which get virtually no real use.

The study begins with the VRLA battery technology primarily used by Gel and AGM batteries and quotes, on page 7/13,  
"Recent industry experience indicates that a 4 to 7 year VRLA battery life is more likely, regardless of cell size or warranty claims. 
In one study of almost 25,000 VRLA cells from 9 different manufacturers, the failure rates ranged from 27% to 86%, depending on the manufacturer. 
These cells were only 3 to 7 years old. The average failure rate was 64% for the entire tested population".

VRLA batteries have been in use in this Industry for many years, longer than in almost any other application.
Despite the manufacturers claiming a 20 year life for these very, very expensive batteries, 64% of VRLA batteries suffered failure in just 3 - 7 years.

What is also interesting is that the failure rate varied between 27% and 86% "depending on the manufacturer"
That is a huge 59% variation in battery manufacturer quality, showing just how important the choice of battery manufacturer can be.
The report continues :

"A European study of over 1,000 installations, of various system voltages and cell capacities, containing about 35,000 cells concluded that VRLA batteries require replacement after 5 to 8 years of operation. Absorbed Glass Matt-type cells demonstrated a higher failure rate than did gel-type cells.  
It was concluded that 20-year class AGM cells actually have an expected life of 5 years at 25°C (77°F), dropping to about 3 years at 32°C (90°F)".

Bear in mind that these are not ordinary '3 year life' High Street AGM's, these are very, very expensive 20 year life rated batteries yet lasted as little as 3 years. 

The above mentioned report then publishes a chart, see a copy below, that shows the reasons for battery failure by battery technology/Type. 
Grid/Plate corrosion accounted for 86% of all Wet acid battery failures and 59% of failed AGM and Gel batteries, clearly Grid Corrosion is the biggest issue for all Lead Acid battery types. Controlling Grid corrosion can be a major step forward in improving battery life.

"Drying out" destroyed an amazing 33% of AGM/Gel batteries, but only 1% of Wet/Flooded batteries   
There is a common belief that Gel and AGM batteries don't lose fluid, so this is a myth firmly dispelled. 

'Cell shorts' accounted for 10% of Wet battery failures but less than 1% for AGM/Gel. 

So now we know some of why Batteries fail, lets look at how usage sometimes has a big impact on life.
In the 'Leisure' battery market place we see batteries destroyed from incorrect use. This is possibly because there is so much conflicting advice on 12v Lead Acid batteries.

An examination of the area straightaway throws up two anomalies. The first is that modern '12volt' batteries are actually 13 volts, or close to that, and a modern Leisure battery actually down as low as 12.0v it is pretty much fully discharged, often to the point of being damaged.  

The second anomaly is that different Technology batteries have different voltage ranges of use, yet this is very rarely ever mentioned, let alone documented. A Gel battery has a voltage range of 13v for full charge, down to 12.5v for 50% discharged. 

An old conventional Wet battery has a voltage range of 12.6v for full charge down to 12.1v for 50% discharged.
In both cases, just 0.5v difference between full charge and 50% discharged.
Apart from the chart below, we have yet to find a battery specialist site, or any information on the web, that makes mention of the differeing behaviour of technologies as far as voltage versus discharge state. 

If  you look at the chart below from Yuasa, the biggest battery retailer in the World, you will note that Sealed/VRLA batteries have a 100% charged voltage of 13.0v. 
When they are 75% discharged (only 25% charge is left) it will be around 12.2v. 
An old fashion Lead Antimony battery has a 100% charged voltage of 12.6v. When 75% discharged (only 25% charge  left) it will be around 11.9v.  

A brand new battery, of either technology, accidentally discharged to a voltage of 12v or beyond 80% is likely to have severely shortened life. 

Therefore we suggest you understand exactly what battery technology you have installed, and discharge it accordingly. 
Note that the battery we suggest is used, Varta LFD/Bosch L range, behaves more like a Gel battery is this respect, having a fully charged voltage around 13v. 

The ideal for long battery life is to discharge a battery no more then 30% for optimum life. For a Gel battery that is 12.7v and 12.3v for a Conventional wet battery. 
You can discharge a battery down to 50%, but it's cycle life can be cut by half, even on a specially constructed Deep Cycle battery.
The chart below from Victron Energy shows just how outstanding their batteries are with 4,500 cycle life at 30% shallow discharge.
Yet if you look at the chart, you will see that the greater the depth of discharge, the shorter the life, discharging the 4,500 cycle Gel Long Life to 80% drops it's life to just 1,500 cycles. 
Yet this is a specialist deep Discharge battery. 

This behaviour is not unique to Victron, who are outstanding in the industry, but ALL batteries from all manufacturers.


So Deep discharging a battery can have a massive impact on it's life. 
Now we know what causes a battery to fail and the part usage plays in that, so lets look at how they work and relate that back to the failures to see how we can choose and then care for our batteries.

                                                           So how does a battery work?

This will just be a brief description of a single lead Cell, 6 of which will make up a 12v Battery. 

When two lead plates are placed in a Sulphuric Acid bath, Voltage will be available if you connect an electrical load to each Lead Plate. 
Modern Lead batteries are more than just two Lead Plates. Construction varies, but simply, the Negative 'terminal' usually consists of a porous plate of metallic Lead. The “+” plate consisting mostly of porous Lead Dioxide paste, supported on a thin metal grid.

As the current flows out of the Cell a chemical reaction takes place with the Sulphuric Acid that converts both Plates to Lead Sulphate. 
'Recharging' the Cell will revert the chemical reaction but some of the material converted to Lead Sulphate will not revert back on each cycle. Sometimes Hydrogen and Oxygen is a by product of the chemical reaction.
The more the battery is charged and discharged (Charge/discharge Cycle) the greater the amount of material that will become 'inactive'.
Eventually the amount of material that has become inactive will reduce the the battery capacity, but not necessarily 'failed'. 
A battery in this state might be classed as 'exhausted' with significantly fewer amps hours to surrender on each discharge, but it may not necessarily have failures such as a Cell 'Short', so may not 'lose charge'. 

The above Cell description is of Wet/Flooded construction. 

Gel/AGM Battery Construction
The primary difference between a Wet/Flooded battery and a Gel is that the Suphuric Acid is in the form of a Gel. 
In an AGM (Absorbed Glass Matt) battery the Acid is 'absorbed' in a Glass Fibre Matt between the Plates.  

Both these types of battery also operate 'under pressure', the pressure helping to recombine any Hydrogen and Oxygen back to Water, to reduce Fluid loss. Therefore, AGM and Gel battery types require a pressure valve to control the pressure inside the battery. 
These are commonly grouped together as Valve Regulated Lead Acid (VRLA) batteries. They are also sometimes incorrectly referred to as 'Sealed' batteries even though they are able to vent out fluid past the valve. 
As has been shown from table above, where 33% of GEL/AGM batteries failed from 'Drying Out', it suggests these battery types are far less 'Sealed' than most people realise. They clearly do vent fluid otherwise the batteries would never dry out.

Each time any Lead Acid battery is charged/discharged there will usually be Corrosion at the Positive plate. The amount of corrosion can vary depending on how the battery is used and it's construction. 
Temperature has a significant effect on Corrosion, just a 9 degree rise above 25 degrees can reduce a batteries life by 50%, see page 2/13 in the 'Battery - Lifetime Study'. 

As noted above Corrosion of the Positive Plate Grid is the Primary cause of failure of all Lead Acid battery types, 86% failure rate for Wet/Flooded batteries and almost 60% for AGM/Gel batteries. Corrosion is dramatically accelerated by faster charging OR/AND operation (both Discharge and Charging) at higher temperatures.

The below are two common 'conditions' with batteries, the descriptions of which are lifted from the same Technical Document 'Battery Life Time Work' first mentioned above.

Sulphation is an issue that is often mentioned as a cause of battery failure and usually results from Undercharging or leaving a battery in a semi discharged state.
This results in a harmful buildup of lead sulfate on the plates, called sulfation. Lead sulfate formed as a result of undercharging is inherently different in structure from lead sulfate formed during normal cell discharge. The lead sulfate formed during normal discharge has a very fine crystalline structure that is easily broken down by charging current. The lead sulfate crystals formed as a result of undercharging continue to grow and eventually reach a size that cannot be easily broken down by charge current. Additionally, the lead sulfate crystals physically occupy more space than the original active material. An excessive buildup of lead sulfate can make the plates warp or buckle. 

Hydration occurs in a lead-acid battery that is overdischarged and not promptly recharged, or a battery that remains in a discharged condition for an extended time (such as might occur during long-term storage). Hydration results when the lead and lead compounds of the plates dissolve in the water of a discharged cell and form lead hydrate, which is deposited on the separators. When the cell is recharged, multiple internal short circuits occur between the positive and negative plates. Once hydration is evident, the cell is permanently damaged.

One paragraph of note in the document is this is one that is little documented elsewhere, which we thought showed the depth of knowledge amongst the Authors : 

"The float charge process maintains the positive plates in a nearly fully charged condition, in which the active material is all lead dioxide, PbO2, with very little lead sulfate, PbSO4, present under ideal conditions. 
During discharge, lead dioxide is converted to lead sulfate. However, the chemical reaction is better facilitated when a lead dioxide molecule is located adjacent to a lead sulfate molecule. In other words, the chemical reaction process improves in efficiency as lead sulfatesites are generated. 
During the initial moments of discharge, the chemical reaction is slightly less efficient, with the result that the voltage can dip to a lower than expected value and slowly recover from this voltage dip during the first few minutes of discharge as these lead sulfate sites are created".

One of the issues of VRLA batteries, like Gel/AGM, is that when they deteriorate, debris can obstruct the Valve causing high pressures inside the battery. Sometimes resulting in explosion.
VRLA batteries are also prone to catastrophic failure from 'Thermal Runaway', a phenomenum whereby the battery faults and gets hot, the heat 'fuels the failure' which then causes it to get even hotter, etc. 
Explosion of the battery is sometimes the end result.

While AGM/Gel batteries are often sold as 'Gas Tight' or 'zero Fluid Loss', and allegedly the 'safest of batteries', as Andrew Goodwin's document shows they do lose fluid. Failure can lead to serious consequences. 

Because of the catastrophic nature in which they fail, we believe Gel, but especially AGM, are the least safe of all Motorhome batteries. When there is Wet Acid battery technology available that includes the Gel battery traditional benefits without the disadvantages, it doesn't seem to make sense to pay twice as much money for a Gel battery.  

Although the Failure Chart lists many 'outright' failures, don't forget that that all lead Acid batteries that are healthy, i.e. zero fluid loss or zero corrosion, will still lose capacity each time they are discharged/charged, purely down to the chemistry of a battery. It may hold it's charge and apperar to perform as usual, put the amount of power in each cycle will slowly reduce.
If you add to the mix Postive Plate corrosion, which in Andrew Goodwin's life time study document is the biggest issue for all battery types, then battery efficiencey may degrade still further as it is used.

Chemistry and Physics laws say that a battery of 5 years of age that has been used regularly, can not be any where near 100%, regardless of what an owner claims. 

One of the reports final paragraphs states :

"Flooded cells are typically housed in clear containers so that corroded cells can be easily identified and changed out. Lifetimes of 15 to 20 years are common and cells are often changed out due to their age rather than due to failure".


So now you know how a battery works and what causes them to deteriorate and fail totally.  

You know that :
1. Batteries deteriorate from use, the lighter the discharge the longer the life. 

2. That AGM and Gel often fall well short of the manufacturers lifetime predictions and that fluid loss is a bigger issue than most realised. They are also not the 'safe' battery option as perceived by many.

3. That Positive Grid Corrosion is the enemy of all Lead Acid batteries and the chief reason for failure of all types.

The information above should help you decide what works for your situation, which is unique, the way you use a battery will not be same as anyone else's. Take the time to assess how you use the Motorhome and the battery.
Just because Fred still has a battery that cost £12.30p 15 years ago, doesn't mean the same battery will last as well for you. 

Our suggestion would be to find a Wet/Flooded battery with technology that resists grid corrosion if usability and long life are your priority.
See`our Battery Technology page for ideas.

The below was an attempt some time ago to create an 'simple' explanation of the issues on battery degradation (primarily from corrosion) and how it affects a batteries performance.

Reproduced here in the hope it is of use to someone. Please keep in mind that it is much simplified. 


What is a Battery?

A Battery is just a vessel that stores Electricity, your battery charger puts a lot of electricity into the battery, for you to take out at a later time. Once you have used all the Electricty, you connect the Battery to a charger to replenish what was used. 

Your Fresh Water tank is just a storage vessel in the same way. You put in water that you can later draw out of the Tap. Unlike the Fresh Water tank that allows you to draw out almost 100% of the water you put in, a Battery will waste some of the Electricity during the charge phase. 

A good quality battery will probably give back 95% of the energy that is used to charge the battery up. 

A less efficient new battery could give back only 90% or less. With a tired battery you might need to put in 130Ah of electricity to get out 100Ah. 

Think of the effect that has on your Solar system, it is like covering up 25% of the Solar panel all the time.

A less efficient PWM Solar regulator with batteries closer to 100% efficiencey is going to win out over a MPPT regulator and tired budget Batteries every time.    

To understand how  internal corrosion affects a batteries capability, imagine it as a water tank with a small hole in the bottom. When the tank is new the water that leaks out is insignificant. But as it gets older the corrosion opens up the hole so more water leaks out. So after 1 year you need to put more water in just to keep the tank topped up. 

However, as the tank ages the pipe leading out of your tank from the Stop Tap also corrodes. Small leaks develop all down the length of the pipe. Whenever you open the tap some Water never makes it into the bucket so you need to have the tap open longer, taking more water from the tank to fill your bucket. Although you are still only filling the same size bucket you did 2 years before, half of it spills onto the floor so the end result is a bucket that is much less full than it would have been 2 years previously. So to fill the bucket to the same level requires you to empty the tank more than you did previously.

To fill the Tank back up now requires the Water Pump to force in a greater quantity of water. However, imagine that the pipe from the Water Pump feeding the tank is becoming restricted by 'furring' corrosion, so getting all this extra Water into the tank is also becoming more difficult. 

Not only do we now have to pump in more Water but it has to be done down a narrower pipe and even as we pump it in, it's leaking out. 

The resultant extra work placed on the Water Pump (the Battery Charger in our analogy) causes a significant strain.

That analogy is the best we can think of to show how a Battery behaves over time, as the battery ages (which might only be months on a budget Battery) it is harder to get the power in and you waste more of it getting the power out. Additionally, but not always, it may run down more quickly. 

The above is a simplistic explanation of something very complex but shows most of the issues in normal Motorhome battery use where the Plates have suffered no damage.   Once the plates have suffered damage, e.g. through overheating, Sulphation, Hydration, Antimony poisoning, etc it changes the above significantly.

Because of the way a conventional Plate deteriorates/Corrodes, a Lead Acid Battery (Gel, AGM or Wet) starts its decline from the moment it is manufactured. Hence the importance of buying only freshly manufactured batteries. Conventional Antimony batteries more than most.

What Bosch/Varta have done, to return to our analogy above, is build a Water Tank that is made from a special  alloy. It suffers no tarnishing, has no leaks. The Inlet/outlet pipes are again specially coated, so no corrosion. Varta/Bosch have found a revolutionary way of making the inlet and outlet pipes bigger, with less friction (Silver/Powerframe Technology) so the water flows in and out of the tank much more easily than most tanks made of Lead. The Powerframe technology makes sure they stay this way. 

So now the Water Pump (Battery Charger) has half the work to do over a 5 year period. A nice side effect is that the Tank now fills more quickly. The final Bosch technological trick, is to cap the tank so no fluid escapes by evaporation.

This technology has been Patented by Bosch/Varta, it cannot be copied by any other manufacturer. It really is unique to them, placing them head and shoulders above the rest.

The Truth About Batteries - Battery Life.pdf The Truth About Batteries - Battery Life.pdf
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Lead Antimony Acid batteries Steve Clark.pdf Lead Antimony Acid batteries Steve Clark.pdf
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