Auxiliary battery

[gen1]

Hi all, I'm after some advice regarding a second battery under the bonnet of my NX. The car is two years old and is about to have its 3rd auxiliary battery fitted, when I can decide what to get. The first was a deep cycle wet battery that failed in spectacular fashion within a few months. The second was a "highly recommended" Ultimate AGM, rated for underbonnet use that has lasted 19 months before giving up completely. I'm wondering if the advantages of AGM batteries are being oversold?! I would prefer to stick with an AGM battery given the experience of the first battery and the damage it caused but I'm open to suggestion. I don't think that for the cost involved that 18 months is a reasonable life for an AGM!

[rykiel575]

Maybe relocate the aux battery.

I am thinking of installing a aux battery myself. I have 4 cells of LiFePO4 batteries which are pretty small. I was thinking of installing them flat in the middle row floor and installing a plywood cover with insulation over it to protect them.

If you want to stick to lead acid maybe consider the optima elsewhere.

Also consider maybe something else is killing them like too much depth of discharge or lack of recharging.

[gen1]

it has to stay under the bonnet, as the third row seat well is used for other things. It's getting charged fine, its been checked often enough and up to a month ago was showing fully charged and healthy. It only powers a fridge and a couple of small LED lights under the awning so isn't exactly working hard. At some stage before winter I will be adding a winch and I have my eye on a battery controller from Traxide that will link both batteries for winching.

[Ian H]

When mine gives up, I'll be trying a Lead crystal battery. They claim that they can handle higher temperatures as one advantage.

[nscheg75]

Three batteries failing. I can understand one, but three. Makes me think there's an issue with the charging process....

[Greg Grey Grumbly]

AGM Battery Setup

I had an under bonnet installation in my NT Paj and it churned through the batterys in roughly two years running just a fridge - not all the time,about two months a year.

I suspected that it was overcharging when the fridge was not in use but the heat in the engine compartment is IMO the major battery killer. I’ve installed an AGM with DCDC charger in my new Paj Sport in the rear cargo area so it will be interesting to see how it lasts.

[Dicko1]

When mine gives up, I'll be trying a Lead crystal battery. They claim that they can handle higher temperatures as one advantage.

I,ve looked into these batteries and I,ve come to the conclusion that most of the beat up is advertising bullshit. These lead crystal batteries are 2 decades old and only 1 company makes them. It is also this company that does the most spruiking of their magical performance. If they were such a great leap forward in technology why hasn't Yuasa, Lifeline, Century, SSB, Optima or any other manufacturer jumped on board and produce them. The a fore named battery manufacturers have deeper pockets than the maker of these batteries and as such you would expect them to want a chunk of the pie..

[Dicko1]

I,m on my 3rd battery underbonnet in exactly 4 years. Heat is definately a killer (here in Cairns it is warm-hot everyday). The 2 x 130 AGM batteries in my rear tub are 30 months old and in great shape. The 3 batteries under the bonnet are start batteries but 1 was an AGM that was supposed to be ok under bonnet...it wasnt.. Just get the largest wet cell start battery you can and leave it at that if you dont to change batteries every 2 years. Its bloody hot under the bonnet!!

[farcanal]

My old NP had one auxiliary battery under the bonnet for about 7 or 8 years. Ran the Waco only. I can't remember what it was, maybe AGM but still going strong when I traded the car.

[dbdb]

I've had an optima under bonnet as auxiliary for more than 5 years in 2 vehicles, it's covered more than 150,000 km. No complaints about it's longevity.

[geopaj]

I have a been running simple wet cell deep cycle batteries for years under the bonnet (NL & NT, both with ARB trays and basic Redarc isolator).
They seem to last approximately 4 years but are under $200.
Just check the electrolyte every now and then and, from what I’ve been toy, they handle under bonnet instillations ok.

[sharkcaver]

I've had an optima under bonnet as auxiliary for more than 5 years in 2 vehicles, it's covered more than 150,000 km. No complaints about it's longevity.

My optima starter lasted 6 months I'm not convinced yet, but it's early days.

My AGM in the rear tub fed by a dc/dc is coming up 3 years now and still tests fine (voltage/CCA and Internal resistance). It is used a lot, on average once per month. Had to put it to combined starting/fridge duties for a week when the optima failed.

Small as it is, the oem wet cell starter battery seemed to have better longevity than any aftermarket wet cell I've used. generally I only get 2 years usage with under bonnet mounting.

I know you are using your tub, but unless its for the 3rd row seating, I would replan your packing and place an AGM with a dc/dc there - you wont look back.

[gen1]

sorry for the late reply, I'm having issues logging on to this site through Chrome and Firefox.... Anyway, Im about to fit the third, so I've gone through two. The first one was a well known Australian made deep cycle wet battery that leaked everywhere and made a mess, so Im still reluctant to get a wet battery in there for now... The thing that annoys me about this situation is that the specialist battery retailer highly recommended this battery, it appears on their newsletter as one of the top 5 AGM, and their own specs says a design life of 12 years. After a fiery phone call pointed all this out they have decided to work something out and will get back to me on Monday. I asked specifically about DCDC chargers as I know there are very strong opinions either way and they assured me that for my setup is wasn't necessary, and the manufacturer (they checked) didn't deem it necessary either. The battery had bulged not long after installation, they were aware of it, and it was monitored for quite a while after with no changes to performance, charge rates etc etc. Current theory, and its only a theory with no basis in fact behind it, is that the bulging has altered the internals and the rough road i was on had led to an internal short... So will see how this pans out. I may just end up with two marine or sealed wet batteries under the bonnet yet!

[Ian H]

I asked specifically about DCDC chargers as I know there are very strong opinions either way and they assured me that for my setup is wasn't necessary, and the manufacturer (they checked) didn't deem it necessary either.

I don't understand that. As far as I know, you can't charge an aux deep cycle properly without one because you have two batteries requiring different rates of charge (starter and Deep cycle). It's the DCDC which makes sure the DC battery gets the charge it needs. Otherwise, if it's only a relay, the alternator gets a full reading from the starter battery and reduces the charge before the aux is full.

[gen1]

Ian, there's a whole other discussion to be had about DCDC chargers... There are a few well known companies that specialise in such things and guarantee these chargers are not necessary for a deep cycle AGM to be properly charged in the vast majority of setups. I have followed that advice in a few different cars over the years with variable rate alternators and until the Pajero I've never had an issue getting long life out my auxiliary batteries. Mind you this car has had a multitude of problems over the two years i've had so who knows, maybe the alternator isn't doing its job either!