Where is your aux battery?

Thanks for the reply Peter, but I guess what I was getting at is the fact that anyone who knows even a little bit about 4WD and setting up for camping is that there will probably be a fridge stuck somewhere in the vehicle.

Maybe not in every case, but vehicles with an aux battery under the bonnet and a fridge in the back with a set of drawers would be a very high percentage.
I would like the same percent chance of winning XLotto.

Most of the ads and blurb you read about battery systems doesn't mention not to hook up a fridge to our you beaut 4WD heavy duty battery.

And with the blurb on a deep cycle battery touted for use on 4WD's you have got to read the fine print to see that there is no warranty if under the bonnet.

I understand the need to monitor the battery and don't let it get down too low, but what annoys me is the fact that the batteries are advertised for 4WD heavy duty use, and the main reason to use a second battery is a fridge in my opinion.
Fair enough if you have a winch and you continually get bogged and use the winch, but what else would you hook up to a aux battery that is going to draw quite a bit of power, apart from a fridge.

It would be interesting to see the manufacturers put all the proviso's on the warranty in the same size font as the rest of the ad.

Dave

Peter, why can't they make a deep cycle battery that will go under the bonnet?
I am sure over 80% of vehicles with an aux battery would have them under the bonnet.

Maybe we would have to have a setup like the XJ12 Jags and have a fan on them.

Dave

Dave,

I totally understand where you're coming from.

It can be frustrating if you want to find a suitable product and all you get from some dealers (and from some manufacturers) are false promises made with the intention of trying to sell you a product which isn't really designed for the task involved.

To sum up the properties of the 'ideal' aux battery, there is this wish list:

a) N70 size, so it actually fits in the space provided
b) capable of powering a small portable fridge for 24hrs or longer
c) fast rechargeability to a high state of charge by the alternator
d) temperature resistant to a high degree
e) vibration/shock resistant
f) low internal resistance for occasional high spurts of current (winch, cranking)
g) shouldn't cost more than an ordinary starter battery

How do popular battery designs stack up to this?


wet cell battery:

a) yes, possible
b) yes, possible but only if multi stage charging is done every time after cyclic discharge
c) not possible due to gassing and tendency of active material shedding under low SOC conditions combined with high charging current
d) medium heat resistance, due to gassing and positive grid corrosion
e) medium to good vibration/shock resistance if designed for automotive use, and only during the first few years of its life
f) yes, suitable
g) yes, possible

gel:

a) yes, possible
b) yes, possible but only if occasional topups are performed using a three stage charger
c) not possible because a smaller wire size has to be selected in an attempt to limit the max charging current which is the lowest of all lead acid designs. If this isn't taken care of properly, the battery will gas excessively due to internal Joule heating.
d) better resistance as long as the charging current is restricted, and the charging end voltage adjusted accordingly
e) not vibration/shock resistant
f) battery will deteriorate quickly under high current loads and the terminal voltage dips as a direct result of high internal resistance
g) tend to be expensive

flat plate AGM:

a) yes, possible
b) yes, possible but only if occasional topups are performed using a three stage charger
c) medium acceptance of charge for medium high charging current, some resistance in the wiring still recommended.
d) medium heat resistance
e) medium to good vibration/shock resistance
f) medium, suitable but not ideal
g) only slightly more expensive than a 'wet' starter battery

spiral wound AGM:

a) yes, possible
b) yes, possible but only if occasional topups are performed using a three stage charger
c) yes, possible
d) yes, possible
e) offers the highest shock/vibration resistance of all lead acid designs
f) yes, possible, offers very low internal resistance
g) only slightly more expensive than a 'wet' starter battery

So the answer to your question David, why can't they make a deep cycle battery which goes under the bonnet is.....they can, but not many dealers are prepared to always sell you the most suitable battery for your application.

cheers, Peter

Thanks again for your reply Peter.
Dave

Peter,

Excellent information not readily available elsewhere. Suggest cut and paste into a blog for easier long term access. The level of activity on the forum means that posts here tend to be lost pretty quickly. Saves a lot of typing if you can simply point to a blog!

Cheers

John

thanks for the suggestion John, the blog is life

cheers, Peter

Hi Peter,
What are examples of spiral wound AGM's? Will be looking for some new batteries soon and have never heard of them.

Steve

Steve,

if you can't see my profile in my posts, just google our company name and you will find all the answers.

Spiral wound AGM are the battery of choice for high current applications in demanding environments.
No other lead acid battery design comes close to it.

cheers, Peter