During the 1980s the aircraft industry developed the A.G.M. battery. This was an alternative to the then very expensive Ni – Cad batteries, which were used in naval helicopters and fighter jets. The A.G.M. battery was originally designed to be warm weather and vibration resistant.
A.G.M. is the abbreviation of absorption glass mat. It was given this name because these batteries are made up of mats, in which the glass fibres are woven to increase the surface area. This then allows the A.G.M. battery to work like a lead acid battery, although the electrolyte in the A.G.M. battery will not freely flood the plates, as the glass mats will prevent this happening.
These glass fibre mats do not absorb the electrolyte, but simply hold the electrolyte preventing it from spilling when the battery is tipped over. Although the A.G.M. battery is seen as a rectangular shape case, the plates themselves can be changed into any shape, including flat or even cupped.
As manufacturing processes have become cheaper, these Deep Cycle Batteries (Leisure Batteries) are now used in Motorhomes.
Advantages of an A.G.M. Battery
1.Unspillable. This means if you turn the battery upside down, the electrolyte will not spill out of an A.G.M. battery.
2.An A.G.M. battery never needs any water, and is considered to be maintenance free.
3.A.G.M. batteries do not give off any gas (hydrogen) when being charged, so there is less concern about ventilation when charging them. This allows them to be used safely inside a motorhome.
4.A.G.M. batteries can stand very low temperatures without freezing.
5.These batteries are also very resistant to vibration, due to their sandwich construction.
Disadvantages of an A.G.M. Battery
1.The A.G.M. battery is considerably more expensive.
2.The deep cycle A.G.M. batteries can only be discharged to 50%, whereas the lead acid battery can be discharged to 80%. This means that the lead acid battery can run appliances longer each single charge.
3.An A.G.M battery should not be overcharged, as it will shorten its life or can immediately kill the battery.
Before you all go out and replace your leisure batteries with A.G.M. ones, there are a few other things you should know.
The charging of A.G.M. batteries is different to that of the lead acid battery. The voltage required to charge them is greater, therefore you will need to replace the original motor home charger if it is not programmable. Even if this is the case, you will then need to fit a devise that will increase the charge voltage from your engines alternator. This would then enable you to charge the leisure batteries whilst travelling at the required greater voltage.
| State of Charge | 12 Volt Battery | Volts per Cell |
| 100% | 12.7 | 2.12 |
| 90% | 12.5 | 2.08 |
| 80% | 12.42 | 2.07 |
| 70% | 12.32 | 2.05 |
| 60% | 12.20 | 2.03 |
| 50% | 12.06 | 2.01 |
| 40% | 11.9 | 1.98 |
| 30% | 11.75 | 1.96 |
| 20% | 11.58 | 1.93 |
| 10% | 11.31 | 1.89 |
| 0% | 10.5 | 1.75 |
Is it the battery or is it the charger?
Frequently when LAS are servicing a motorhome, the owner will ask us to check the batteries. This is then followed by “The leisure batteries don’t last very long before they go flat, we only watch the T.V. for a few hours with one light on!” The problem more often than not is the battery charger.
Many American Motorhomes in America are left plugged into an external power source continuously, therefore the manufacturers fit a charger that will not allow the acid in the battery to evaporate, and this also means that no topping up is required.
If you unplug your American R.V. drive it to your holiday destination, then plug it back into another external power supply, you will never know if your batteries are suffering. It is only when or if you do wild camping (this is without an external power supply), that you will begin to notice the short amount of time to discharge your batteries.
We will set out to explain some of the charge and voltages that relate to a 12 volt battery. A 12 volt battery is deemed fully discharged at 10.5 volts at a temperature of 77 degrees F. Below is a table of the state of charge, in relation to the voltage.
At the bottom of the table you can see the state of charge 0, and the voltage of 10.5 as is stated above. If you find that your battery is below 10.5, it may require a recovery charge or replacing.
Many American motorhome chargers will only charge at 12.5 volts, which is suitable for running12 volt bulbs, but as you can see from the chart this will only give you 80% of the charge when allowing for the potential difference. This shows that an American motorhome requires a good charger to look after its batteries.
The charger needs to be able to carry out a bulk charge, an absorption charge, and also a float charge. These three charge methods require performing at the correct voltage, or the process will be deemed useless.
Bulk Charge
This is the first stage of charging and shows what a fully discharged battery will go through. The battery charger fitted to your R. V. should have a maximum charge rate of 10% of the total battery, or the batteries capacity. 4 x 100 amp hour batteries will require a 40 amp charger.
If we use the above as our example the charger will charge batteries at 40 amps current, until the voltage rises in the battery to 80 – 90% fully charged. As you can see from the table, the voltage will be between 12.42 and 12.5. To allow the battery to reach this voltage, the charge voltage will be around 15 volts. There is no correct voltage for bulk charging, that is why the 10% of total battery capacity is important. It is essential not to supply the battery with too greater current and damage it.
Absorption Charge
This is the second stage of the battery charging. At this stage the voltage remains constant and the current gradually tapers off, as internal resistance increases during the charging process. It is during this stage that the charger puts out maximum voltage. Voltages at this stage are typically around 14.2 to 15.5 volts.
Float Charge
This is the final stage of the charging. After the batteries reach full charge, the charging level is reduced to a lower level (typically 12.8 to 13.2 volts). This reduces gassing and prolongs the battery life. This stage of charging if often referred to as a maintenance or trickle charge, since its main purpose is to keep an already charged battery from discharging.
If your American motorhome has a good charger fitted, you should get 4 to 6 years battery life, but often you will find that the poor battery chargers will require you to change the batteries about once a year.
As batteries age, their maintenance requirements also change. This means longer charging times and/or higher finish rate (higher ampage at the end of the charge). Usually older batteries need to be watered more often, and their capacity decreases.
If you have any questions on batteries or battery chargers, do not hesitate to contact LAS Motorhomes on 01604 861999.
FAQs
Are AGM batteries good for motorhomes? ›
A.G.M. batteries do not give off any gas (hydrogen) when being charged, so there is less concern about ventilation when charging them. This allows them to be used safely inside a motorhome.
What is the main disadvantage of an AGM battery? ›The main disadvantage of an AGM battery is the up-front cost, when compared to a traditional flooded lead-acid battery.
Are AGM batteries worth it for RV? ›Firstly, they hold their charge better. Secondly, they are less likely to sulfate when compared to normal, wet cell batteries. This is incredibly beneficial for vehicles that are not used regularly, meaning that they are perfect for RVs that are sat idle for long periods of time.
What is the best battery for RV house batteries? ›- Optima Batteries YellowTop Dual Purpose Battery. ...
- Renogy Deep Cycle AGM Battery 12V. ...
- Expert Power 12V Rechargeable Deep Cycle Battery. ...
- Optima Batteries D51 YellowTop Dual Purpose Battery. ...
- Interstate Batteries 12V Deep Cycle Rechargeable Battery. ...
- Optima Batteries 12V YellowTop Dual Purpose Battery.
Many AGM batteries will last two to three times as long as their flooded counterparts, so from that perspective it seems to at least make sense. When you add in the safety benefits of an AGM battery on top of the performance benefits, AGM batteries make even more sense.
What's the best AGM battery for a RV? ›- Weize 12V 100AH Deep Cycle AGM Battery. Specs. Price: (fewer = cheaper) ...
- Universal Power Group 12V AGM DEEP Cycle Battery. Specs. ...
- Mighty Max 12V AGM Battery. Specs. ...
- Lifeline AGM Battery – GPL-4CT. Specs. ...
- Mighty Max Battery12V 35 AH SLA Battery. Specs. ...
- Lifeline Marine AGM Battery – GPL-27T. Specs.
When you partially charge AGM batteries, they with time lose their capability to charge to full capacity. If you constantly charge your AGM battery to only 60% for instance, it may eventually fail to charge past 60%. This, in turn, reduces the lifespan of the battery.
What happens if you charge an AGM battery with normal charger? ›AGM batteries require a slower, more stable charge than flooded batteries and can't sustain the high charging speeds used by standard battery chargers. If you charge an AGM battery with the wrong type of charger, you will end up under or overcharging your battery.
How do I keep my AGM battery healthy? ›- Storage. Never store your battery in a discharged state, this can cause sulfation (see below) and make it difficult to recharge the battery fully. ...
- Preventing Sulfation. ...
- Charging Your Battery. ...
- Using a Battery Charger. ...
- Charging From Solar.
If you're looking for a sturdier battery, switch to an AGM battery. Originally developed for use in aircraft and military vehicles, it's designed with ruggedness in mind. So its sandwiched mats and plates can handle shocks much better than a standard battery. It's also more resistant to vibration.
How long do AGM batteries last in RV? ›
An average use of seven years is perfectly normal for 12-volt Gel or AGM batteries.
Can AGM batteries be fully discharged? ›AGM's have a very low self-discharge - from 1% to 3% per month is usual. This means that they can sit in storage for much longer periods without charging than standard batteries. The Concorde batteries can be almost fully recharged (95% or better) even after 30 days of being totally discharged.
Which RV battery lasts the longest? ›How long should the best RV battery last? A typical lead-acid battery, when maintained correctly, can last up to 5 years or more. Lithium-ion batteries and AGM batteries can last longer than that. Lead-acid batteries do not last as long as other, more expensive batteries.
Should I leave my RV plugged in all the time? ›Is it Okay to Leave Your RV Plugged in All the Time? Again, the short answer about keeping your RV plugged in all the time is – no. The risks include battery damage from overcharging and frozen refrigerator coils, as most RV refrigerators need to be periodically cycled off and thawed.
Why is my AGM battery draining so fast? ›Whether you're using a car battery, AGM battery, lead-acid, or lithium battery, a decline in performance and faster discharge rate are usually caused by similar issues. These include battery age, over or undercharging, exposure to extreme temperatures, or sulfation.
Can you charge AGM battery with alternator? ›Charging From Your Vehicle Alternator
In general car or van alternators work reasonably well with Lead Acid and AGM batteries.
If the charge level of a fully charged AGM battery is less than 20% of a fully charged voltage level, the battery could have been damaged by sulfation, overcharging, or undercharging. It can be improved using a desulfation device or by just replacing the battery.
How do you maintain AGM RV batteries? ›- Storing your AGM battery. When you are storing your AGM battery for longer periods, always remember to recharge. ...
- Sulfation prevention. ...
- Do not overcharge the AGM battery. ...
- Use the manufacturer's recommended charger.
Absorbed Glass Mat (AGM)
AGM batteries are not subject to the same charging restrictions as gel batteries, so, generally, standard RV charging equipment can be used without modification.
AGM charge current should be between 0.10 and 0.15 of the20 hour rate AH rating. So a 100 AH battery should be charged at between 10 and 15 Amps.
Can you jump start an AGM battery? ›
Your One-Stop Solution for AGM Service
As mentioned above, jump starting AGM batteries is very straightforward. That said, our Booster PAC and Jump-N-Carry traditional jump starters use AGM batteries in them and are legendary for their power and durability.
Are there any advantages of using AGM batteries over well cell or gel cell in the summer? TPPL AGM batteries, such as ODYSSEY® Extreme Series™ batteries, are designed specifically for high temperatures. They can reach up to 176°F (80°C) and not lose internal water, as the battery remains sealed during its operation.
Can you charge an AGM battery too often? ›Overcharging an AGM battery can lead to reduced battery life. Many modern chargers allow you to select whether you're charging an AGM battery or a flooded cell option.
Is it OK to use a trickle charger on an AGM battery? ›Many GEL, AGM and Calcium's are better than regular lead-acid batteries but even so you should charge them back up regularly, or better still use a trickle charger (or solar panel) to keep them in top condition and extend their life.
Does cold weather affect AGM batteries? ›AGM batteries can function well below freezing, although all batteries can freeze if it gets cold enough. AGM batteries need to be examined and maintained while they are stored over the winter, even though they are maintenance-free and perform well in cold conditions.
Do I need a special charger to charge an AGM battery? ›You will want to find a charger that puts out at least 5.5 amps, but ideally 13-14 amps. If you have 2, DC55-12's in a parallel string (12V, 110Ah) you'll need at least 11 amps, but better if you have 22 amps. Conversely, you don't want to throw too many amps at the battery, or you'll run the risk of an early failure.
What is the average lifespan of an AGM battery? ›A properly maintained AGM battery usually lasts somewhere between three and four years, but this depends on the amount that you use it. Also, the amount that you drive your vehicle plays a role in how long the battery will last.
What voltage should an AGM battery be when fully charged? ›AGM batteries are designed to require 14.6v – 14.8v when performing a full charge from a state of discharge, whereas standard lead acid batteries need 13.8v – 14.4v, hence this is what most onboard chargers are designed to deliver – not the 14.6v – 14.8v that AGM requires.
Can an AGM battery last 10 years? ›We can generally say an AGM battery can last two to three times as long as a flooded battery. In the commuter car example we referenced, if a flooded battery lasts three to five years, an AGM battery could last six to ten years or longer.
How many cycles do you get out of an AGM battery? ›A standard 12 volts gel or AGM battery can carry up to 500 cycles of charge and discharge, considering that it will be charged from at least 20% battery level. Even after the six-year period is over, you might not need to replace the battery urgently as it can still be used even at 50% of its capacity.
How long should I charge my AGM battery? ›
Most AGM batteries hold 100 amp-hours. In this case, a 10 amp charger would be perfect, taking between two and nine hours to fully charge your battery, depending on how much it has depleted. Chargers with higher amps will charge faster, while those with lower amps will take more time.
What voltage should I cut off AGM? ›The truth is that any lead acid battery, be it a Gel Cell, AGM or flooded batteries such as DCBs, should be cut-off at 11.6 volts. Not doing so increases the risk of damage to the battery and if taken down deep enough into the batteries charge, will ruin the battery.
Can I replace lead acid battery with AGM in my RV? ›Yes, not only can you upgrade your Lead Acid batteries to AGM we also highly recommend it. In order for Lead Acid batteries to maintain their charge, they need maintenance.
What kind of battery goes in a motorhome? ›If you have a motorhome, you'll have a chassis battery for starting the engine and at least one 12v deep-cycle house battery, or two 6v deep-cycle house batteries. If you have a travel trailer or camper, you will have a deep-cycle battery (or batteries) only.
Should you leave your RV plugged in all the time? ›Is it Okay to Leave Your RV Plugged in All the Time? Again, the short answer about keeping your RV plugged in all the time is – no. The risks include battery damage from overcharging and frozen refrigerator coils, as most RV refrigerators need to be periodically cycled off and thawed.
Do you need to vent AGM batteries? ›Even though AGM batteries are considered to be maintenance-free, they still require venting. If you overcharge the battery, charge it too quickly, or don't allow enough AGM battery ventilation for the absorption mat to keep up with, the same dangerous build-up of hydrogen gas can occur.
How to choose a battery for an RV? ›- Amp-Hour Rating. The amp-hour rating will inform you how much electric capacity that battery has. ...
- Required Maintenance. ...
- Expected Lifespan. ...
- Cost Of The Battery. ...
- Anticipated Motorhome Usage. ...
- Flooded Lead-Acid Batteries. ...
- Absorbent Glass Mat (AGM) Batteries. ...
- Gel Cell Batteries.
A fully charged leisure battery will show a reading of 12.7V or more. Anything less than 12.4V is deemed as deeply discharged and the use of a smart charger is advisable. State of health testing should be carried out using a suitable conductance type tester.
Which battery starts the generator in a motorhome? ›Motorhomes typically have two types of batteries: chassis batteries and house batteries. Chassis batteries are used to start the engine and run the chassis components like exterior lights, turn signals, etc.