Camping AGM as starting battery

[ytt105]

I'm about to upgrade the caravan battery to Lithium, and I don't want to waste it's existing 100ah AGM.

Can I use it as a starting battery for my D4?

Regards
Trevor

[Tombie]

Depends on its size… and type….

What model designation is the battery?

[reefmagnet]

Heat destroys AGM. Definite no if the engine bay will be where it's located. Other than that maybe.

Another idea is to use it as a failsafe for the lithium's if you have the room. The reason for this is lithium batteries can disconnect at the drop of a hat and a big old AGM as a backup will help keep the lights on.

[101RRS]

Heat destroys AGM. Definite no if the engine bay will be where it's located. Other than that maybe.

Yet later D4s use a AGM as the starter battery - hence I guess Tombie's question on the battery details.

[PhilipA]

A dual purpose AGM for starting and deep cycle will have a CCA rating somewhere on it.

Usually a 100AH deep cycle will have about 650CCA.
Regards PhilipA

[reefmagnet]

Yet later D4s use a AGM as the starter battery - hence I guess Tombie's question on the battery details.

Some AGM's are rated for under bonnet use. Spiral wound like Optima comes to mind. I use one in the engine compartment of my boat and it's fine. A camping AGM, perhaps not.

[drivesafe]

Hi Reefmagnet, as others have indicated, hybrid AGMs can be used in the engine bay and there are quite a few of them now days.

Hi Trevor, as others have pointed out, check the info on your AGM.

If the battery has both an Ah ( Amp Hours ) rating and a CCA rating, then you have a dual purpose AGM and it will be fine to use as a cranking battery, if it fits.

If your battery only has an Ah rating, then it is a dedicated DEEP CYCLE battery and can not be used as a cranking battery. To do so will mean your battery will have a very short lifespan.

[reefmagnet]

Your basic deep cycle AGM battery also doesn't take kindly in the long term to being charged and maintained at flooded lead acid charge voltages. They also don't do as well in situations where they don't receive a regular decent absorption charge.

AGM main benefit over FLA is that it is spill proof and doesn't out gas during charging. Other than that, the longevity advantage only applies if they are used with kid gloves.

But if it is at least a dual purpose, it may be ok.

[DiscoJeffster]

Your basic deep cycle AGM battery also doesn't take kindly in the long term to being charged and maintained at flooded lead acid charge voltages. They also don't do as well in situations where they don't receive a regular decent absorption charge.

AGM main benefit over FLA is that it is spill proof and doesn't out gas during charging. Other than that, the longevity advantage only applies if they are used with kid gloves.

But if it is at least a dual purpose, it may be ok.

You missed the biggest benefit of AGM. Their design means they tolerate deeper discharge more often with less long term damage than flooded. This is why LR switched the D4 to AGMs.

[reefmagnet]

You missed the biggest benefit of AGM. Their design means they tolerate deeper discharge more often with less long term damage than flooded. This is why LR switched the D4 to AGMs.

It's just my opinion of course, but I would say that is true only if the batteries are treated very kindly. A dedicated start battery "on paper" should have benefit from a long life because starter batteries are rarely deep discharged. However we're talking about a (presumably) deep cycle and quite possibly generic AGM which is a different kettle of fish. Aside from the obvious issue of using a deep cycle for starting (which works, just shortens the life as has already been previously noted), deep cycle AGM's should not be discharged below 30% for maximum life and taking them below 50% depth of discharge too many times will shorten the recharge cycles considerably. I'm not against AGM per se. In fact, I have two deep cycle house banks and a starter on my boat, all AGM. The house banks are coming up to 8 years old now and still going reasonably strong but I pamper them because I've also thrown out a few near new units due to previous owners using them in the wrong applications - including engine bay installation of deep cycle AGM. FWIW, Century deep cycle AGM's actually have written on the battery label itself that the warranty is void if installed in an engine compartment.

A few years back, AGM were the next best thing. They were the ones demonstrated submerged upside down in fish tanks at the caravan and boat shows, but time has shown they do have their quirks. Be that as it may, the AGM I would trust for an under bonnet install would be one specifically designed with that purpose in mind and labelled as such. Even then, the physical properties that makes them susceptible to heat damage is never really resolved, it simply means the batteries are at least designed to tolerate the environment better.