Is Long Term connection to Electric Mains Hook-Up/Solar Good or Bad?

"My leisure battery exploded last week. The camper was on EHU at the time. Is it possible for me to send you the Calira for diagnostics and repairs? I am based in Oxford. Regards Sarah."


Sarah's Calira charger was damaged beyond repair, really bad Acid damage. 

We have been writing for a while that long term charging of Motorhome Habitation batteries is not ideal for either the charger or the battery. 

Regardless of what you believe, Sarah's exploding battery tale above at least indicates that charging any battery long term unsupervised can have serious consequences.

All the big battery manufacturers state that any battery on long term Float, Maintenance, Trickle charge or whatever you want to call it, should be maintained between 13.0v and 13,2v not the 13.8v charge rate of most Motorhome chargers. 

Charging permanently at 13.8v causes battery corrosion and shortened life. 

The Yuasa website states that Leisure batteries kept on a permanent 'float'/'trickle'/'maintenance' charge, "will result in internal degradation of the battery". Even when used with, "a well-controlled charging system". 

As a result they suggest that batteries treated this way should be regarded as having a maximum two year life. See this extract :

Battery Maintenance in Non-Automotive Float Applications

1.Typical applications are motor-generators, stand-by applications etc. The Leisure Battery range is recommended for these applications; standard vehicle batteries are not suitable.

2. Batteries used in these applications should be changed every 2 years or more frequently. (Continuous charging, even from a well-controlled charging system, will result in internal degradation of the battery).

For full text read here :

Additional evidence to support things are not well with all Motorhomes in this respect is the tale with Banner Energy Bull batteries.

The Banner Energy Bull Wet battery seems to be prone to fluid loss in normal circumstances, but this seems to be much worse when on long term charging, either by connection via EHU or Solar power.

Back in 2014 the Roadpro website was stating that the Banner Wet batteries were Maintenance free,

                   Banner Energy Bull” batteries don’t require maintenance in normal use"

However, as of November 2016 the Roadpro website had changed to warn of high fluid loss when used : 

                         "'...... with a solar panel, a battery to battery charger or a mains charger that's on for days at a time, the electrolyte levels of Energy Bull batteries must be checked on a regular basis".

Normally, excessive fluid loss is a sign of overcharge. Clearly these batteries are losing a lot of fluid when on Solar and long term mains charging, strong evidence that long term charging from Solar/EHU affects batteries.

While the Banner Energy Bull has clearly been highlighted, the issue affects almost all Habitation batteries to some degree or other.  

Note also that as of 07/04/2018 the Banner website was stating that their Banner Running Bull AGM batteries should not be left on charge for long idle periods, i.e. more than 7 days at a time or the battery life will be shortened. The FAQ page has an item :

"What values should I use when setting an external charger for AGM batteries in the caravan? How high should the charging and float charge voltage be?

Please employ the AGM setting, which means that the charge voltage should be set at max. 14.8V and the float charge voltage at 13.5V. Best of all, use an IUoU characteristic with temperature compensation (should you have this setting available). In order to obtain the maximum service life from your battery, please ensure complete separation from the on-board supply (charger) when the vehicle is not in use >7 days.  

We think the majority of people believe that their Motorhome battery charger (either Mains or Solar) shuts down totally when the battery is full. Yet many of the chargers we repair continue to 'force feed' the battery, albeit at a low rate, even when the battery is at maximum capacity. 

For example one Solar Regulator we encountered recently 'wakes up' each day when the Sun rises and then goes straight into a 'fast charge' 14.7v for a fixed time of 2 hours, even if the wet acid battery is already fully charged. 

It will only drop to a 13.8v 'trickle' charge once the 2 hour timer expires. That will happen 365 days a year. And yes the quote of 14.7v for a wet acid battery is as per it's spec, not the usual 14.4v, so this again will have an 'overcharge' impact.

That will seriously shorten any batteries life if the Solar isn't managed by shutting off manually.

Full details of the Solar Regulator here :

The behaviour of this Solar Regulator above is not unique. We don't know of a single Solar Regulator that 'wakes up' each morning and automatically goes into the battery charging state it was at the night before when the Sun set and the Regulator ceased charging. 

For example most Motorhomes will spend at least 50% of the year unused, so the batteries will be full. In these circumstances most Solar regulators will end the day in a 'trickle' charge mode, yet when they power back up the following morning when the Sun comes up, almost all we have seen go into a 'fast charge' mode for a fixed time period, sometimes as much as 4 hours, even if the battery is already fully charged.

The worst offenders are the Solar Regulators designed for 'House Roof' Solar' solutions as they often assume, correctly for a House system, that the owner wants 100% to be thrown at the National Grid. Therefore their design is to start-up and work flat out. 

On a European Motorhome specific Solar Regulator, they are designed on the premise that the battery will be fully charged much of the time. Additionally they 'trickle' charge at a much lower 13.4v. See our Solar Power pages for the Solar Regulators we recommend.


Similarly most motorhome mains 230v chargers do not 'turn off' as many believe, but drop into a low charge mode, still constantly drawing 230v mains electricity and putting around 13.8v into the battery. 13.8v is fine to 'trickle' charge for a few weeks, but not months or years.


We also see signs inside the battery chargers we repair, that shows they are either not designed to run 365 days a year or suffer if they do. See bottom of page for more info on this.

Victron Energy, manufacturers of top quality Long life Motorhome batteries, are also suggesting that the 13.8v charge voltage of the average motorhome charger will shorten a batteries life. The 'Victron Energy Unlimited' document, see below, suggests a maintenance charge of just 13.0v - 13.2v. 

In installations where batteries are kept on permanent charge, like UPS battey backed installations for Hospitals, Data Centres, etc the recommended maintenance/trickle voltage from the Battery manufacturers is between 13.0v and 13.2v.


Schaudt's latest LRM1218 Solar Charger has dropped the Maintenance charge down from the previous units 14.2v maintenance charge to just 13.4v. 

Victron Energy's own new range chargers now Maintenance/Float/Trickle charge at 13.2v, suggesting as per other documents now surfacing, that long term EHU at the usual Chargers 13.8v will have consequences.

The Author of the Victron Energy Unlimited document writes, 

"The flooded battery types that have been discussed have not been designed for float charging over long periods of time (i. e. several months or years). When float charged at the higher end of the 12.9v to 13.98v range, service life will be shortened due to corrosion of the positive plate grids, and batteries with a high antimony content will need frequent topping up..... 

When float charged at a low 12.9v, aging and gassing will be under control, but a regular refreshing charge at a higher (absorption) voltage will be needed to maintain the fully charged state. 

In other words: the high end of the 12.9v to 13.98v range is fine for a few days or weeks, but not for a 6 months winter period. To my opinion, instead of trying to find a delicate balance between insufficient voltage to compensate for self-discharge and too much gassing at a higher voltage, it would be better to leave the battery open circuit (off charge) and recharge regularly. Depending on temperature, at least once every 4 months or to reduce float voltage to a very low level, for example 13 V".

He goes on to write that Gel batteries are more tolerant of a higher Float/Trickle/maintenance charge. 

However, there is evidence that even these will last longer if not long term 'Float' charged. Just left to settle, then re charged at intervals like that suggested for Wet Acid batteries. 

He writes, 

"All VLRA batteries mentioned can be float charged for longer periods of time, although some studies have shown that a treatment similar to the one proposed here for flooded batteries will increase service life (see, for example the document, “Batterie Technik” by Heinz Wenzl)".

The full text can be viewed in the document below, section 4.2.

Victron Energy-Unlimited Battery Bible.pdf Victron Energy-Unlimited Battery Bible.pdf
Size : 599.973 Kb
Type : pdf

The Batteries most degraded by constant EHU charging are the ones that use the very technology often adopted for very Deep Discharge batteries in Motorhomes : Lead Antimony batteries.

A paper by battery expert Steve Clark, see bottom of page for full report, states :

"Today, Antimony alloys dominate the market for cycling applications and due to ease of production are common in developing nations. The dominance of Antimony alloys in the cycling market is based on the fact that the alloy is extremely resistant to distortion or damage from repeated discharge and recharge cycles".

However, he goes on to say that they should not be 'constant charged' :

"Lead-Antimony alloys are not well suited for stand-by service with a constant charge. The phenomenon of antimony-poisoning where antimony from the grid alloy forms small discharge points on the negative plate surface is a direct result of continuous charging. This results in a continuously increasing float current and water consumption over the life of the battery. The rate of antimony-poisoning is directly related to the operating temperature, charging voltage and the antimony content of the alloy".

This Antimony Poisoning is in addition to the accelerated corrosion they will most likely endure.

We think that the likes of Trojan, Rolls and other specialist manufacturers of ultra Deep Discharge batteries are probably the ones most affected by Antimony poisoning from long term charging? 

We therefore suggest that you research very carefully the technology inside any Battery you intend to match with Solar or keep on long term EHU. 

Clearly, Lead Antimony based Deep Cycle batteries will degrade very quickly if subjected to charging they were never intended to endure. Their life will be shortened and Water loss may be high.  

Here is a very dry one we found  earlier :


Lead Antimony Acid batteries Steve Clark.pdf Lead Antimony Acid batteries Steve Clark.pdf
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Type : pdf

The above documents the impact on batteries of modern chargers, yet old technology, low power output chargers may not be so damaging. 

Some Motorhomes, especially British made prior to 2009, tended to have low power chargers, like a fixed 13.5v low current charger. These will obviously have a far less drastic effect on a battery left on permanent charge. Therefore the above comments won't necessarily apply in full to all Motorhomes. 

The overall damage to the batteries will depend on the duration, the charger, the battery make, condition, the equipment installed in the Motorhome and technology.

Temperature is also a key factor, a Battery continuously Float charged in Iceland may not suffer damage but a battery Float charged during a hot Spanish Summer for just a few Months may suffer significantly. I would venture to suggest that a battery continuously Float charged by a Solar Regulator in Southern Spain might deteriorate more than a battery in Stornaway kept on EHU through the Winter? 

No two Motorhomes will behave the same even if they seem similar.

It really is very Motohome specific.

The new Victron Blue Energy 20A battery charger has a new charging stage, over and above the usual 3 stage charger units, called 'Storage Mode', perfect for Motorhomes.

The technical document states :

Storage Mode = less maintenance and aging when the battery is not in use :

The 'storage mode' charge program kicks in whenever the battery has not been subjected to discharge during 24 hours. In the storage mode, float voltage is reduced to 2.2 Volts/cell (13.2 V for a 12 V battery) to minimise gassing and corrosion of the positive plates

Once a week the voltage is raised back to the absorption level to ‘equalise’ the battery. This feature prevents stratification of the electrolyte and sulfation, a major cause of early battery failure.

Victron Energy are one of the few Battery Manufacturers who also manufacture chargers, hence their depth of understanding of both. One of the reasons we think they are ahead of the competition in this area. 

Ask yourself why they think there is a need for a specialist low voltage 'Storage mode' to protect batteries, if the old myth that you can leave any battery on permanent long term charge is true? 

If you want to learn more about batteries try our 'How Does a Battery Work?' webpage.