Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Exide AGM 12-31 reliability

There have been five cases, that we know of, of battery failure with Exide AGM 12-31 batteries recently. The failures have been total and without warning, other than a slight misfire before stopping entirely, resulting in the cars ending up at the side of the road with no power at all. One also involved the rectifier failing but it is not clear if this was as a result of the battery failing or the cause of the battery failure. The others were fixed with replacement of the battery alone. It's not clear what the problem is with the Exide battery, maybe a bad batch but...... Most of the replaced batteries were not kept for investigation as they were changed under less than perfect conditions. The batteries have worked fine, some up to 18 months, before failure without warning. Most seem to have used battery conditioners with "AGM" selected.

This is bad news as this Exide battery looked like the ideal M3W battery, the correct size, AGM construction, good capacity and all at a reasonable cost. There are a number of suggested batteries on the Alternative Parts List. I have used a Lithium Ion battery for over 6 years now without any issues (kiss of death warning) but they are not cheap.

Thanks for this warning - timely as we are preparing to head off for the Treffen...our Exide AGM is at least 4 years old (albeit mostly run with CTEK on bike/AGM setting when resting)....change or not???

Other than the 5 cases we know about can you let me know if you have had an Exide AGM 12-31 battery fail please, not just go flat slowly but fail totally and quickly. If you have please say when the battery was bought and fitted approximately, just to see if this is a problem confined to batteries of more recent manufacture.

It unfortunately comes down to our expectations for a battery, we want small size, lots of CCA's and expect longevity. And all of this in a vehicle with suspect electronics at times. Lead acid batteries are not complex but you cannot have all three. (and an AGM is really just a lead acid battery, but they are absolutely not forgiving of being discharged.

On a trailer forum I saw someone claim he had DEEP CYCLE AGM batteries. It said so on the side! I offered him some beach front property in Arizona.

Being of a curious nature and having bought deep cycle batteries for a boat many years back, I was curious to find out if AGM batteries were not available as deep cycle types by reason of their internal make-up. I googled AGM deep cycle batteries and it seems there are many advertised as such...?

I`m no battery expert however as best I understand it deep cycle batteries are designed to hold their charge longer than standard lead acid batteries during periods of inactivity thus perhaps more designed for Boat, caravan and other similar usage situations..?

These days with some vehicles being left unused for weeks if not months at a time, I suspect there may be just a bit more chance of firing it up when needed after lay-up if it has a deep cycle battery fitted...?

With the ability to attach an automatic float charger during periods of lay-up, there seems little requirement to pay extra for a battery with deep cycle functionality..? Or have I got that all wrong..?

Lead acid batteries are pretty simple: I wonder what the cause of failure is?
https://www.batterystuff.com/kb/articles/battery-articles/how-do-batteries-die.html suggests heat, vibration, overcharging... I wonder if the latter is an issue with the M3W regualtor? If so are there some electronics that would help?

Apologies for correction George but just wanted to explain the substantial difference between a true deep cycle battery with the other extreme, a cars starter battery.

A deep cycle battery has a lesser number of thick plates for any given size allowing the electrical to chemical energy conversion to be stored deep into them. This makes the battery very robust in terms of longevity as it allows discharge to low levels without undue damage, hence the name. It does mean that charge and discharge currents are lower so take place over a longer period of time. The main reason is the much reduced electrolyte to plate surface area since it's at the surface of the plates that the electrical/chemical and vice versa conversion takes place. It also takes a finite amount of time for the chemical change representing the electrical charge to sink deep into the plates composition and of course vice versa when it's asked to discharge back into electrical energy. This makes them ideal for boat or home overnight storage where they would typically be part of a battery bank dissipating the charge/discharge current to a modest level between batteries.

A starter battery by comparison is a single battery required to give a very large current for a short period of time, typically seconds. This is achieved by a large number of thinner plates giving a much greater surface area of electrolyte to plate interface and so accomodating the high current demanded. Although seemingly more fragile it achieves reasonable longevity by light use, typically discharging to only 10% or less of fully charged capacity before the cars alternator tops it back up to 100% again. A true deep cycle battery would therefore be compromised if used as a cars start battery.

There is a halfway house known as the leisure battery popular on caravans and campers although favouring start battery requirements.

The above relates to AGM or normal lead/acid construction although deep cycle requirements favour the latter.

Richard, Apologies..??? I am grateful for the education you provide. Truth be told, that is why I post the questions... (-: My real issue is the lack of ability to remember that which is imparted. )-:

I have just heard of another Exide AGM 12-31 failing completely in use, this time on a motorway near Hamburg. It seems that there is certainly a problem with these batteries in M3W's. At least two of them have killed the rectifier at the same time as failing. If you have one of these fitted it would be worth considering a change, particularly if it has been fitted for about two years or less as these failures have all been in that range.

Or could it be the rectifiers killing the batteries?