.....and another battery query

I was on a website the other day and it listed and described various batteries. I was looking at the Fullriver and it clearly said that it was an agm yet suitable for the engine bay. It stood out because it flies in the face of the general consensus that this is not the case. I suppose there's always the possibility that this supplier might have nit wrong. Perhaps somebody is aware of it?

Gday Frank,
I have a scangauge too - the voltage reading on it is not accurate - most times it underreads by the best part of 0.3V. That's comparing it to an accurate digital voltmeter reading off the battery terminals. So if yours is anything like mine, when your scangauge says 13.1V, the battery voltage is most likely 13.4V.
Great device otherwise.

Cheers
phil

ha - I had the voltage at 13.2. Anyway, not really enough. I am looking into the dc dc solution. Is this a ...erm.... "current" (pun intended) trend with modern cars? I take other vehicles have the same issues? I might also add, my previous fridge was a waeco, which was less demanding and I had not issues with it, so I'm wondering if it's the Engel with it's heavier demand. It has been suggested that it doesn't take much to stop them working if supply isn't all it should be.

Hi Phil,
Very interesting comment. I would have thought that the OBDC codes as interpreted by Scangauge would have been pretty accurate. But I suppose it's all in the interpretation as coded by Scangauge's engineers. I'll check mine tomorrow.

In any case IMO, from what I have read and studied, 13.4V is still not enough to do the job properly for an aux battery where you probably want the max depth of charge, and it's a compromise even for a crank battery.

Cheers

Gday Frank,
I run a separate voltage measuring wire at each battery and hook them up to a decent voltmeter inside the car so I get an accurate reading at each battery and know what's happening. I was surprised at how much the scangauge was out, and I expect its because its reading voltage from the same tiny wire that is drawing current for the unit or supplying the ECU.

The optimal charging voltage of a battery varies with temperature - the warmer the environment, the lower the required voltage. So lower voltage under the bonnet is appropriate. Mine starts at 14.15V when cold and settles at about 13.5 when the motor is hot. My voltage also varies with revs - at 500rpm idle it usually reads lower than at 1500rpm so if you're measuring voltage, do so when the vehicle is driving. As far as the cranking battery goes I think that's all OK on most vehicles.

Problem with auxillary batteries is that if the battery is installed in a cooler environment (eg in trailer or back of car) the temperature regulation is no longer appropriate. But an auxillary under the bonnet usually charges up OK if given enough time. The wet cell deep cycle batteries are usually Calcium-Calcium and need higher charge voltages and don't charge well with the low vehicle voltages. They need to be topped up via a Dc-dc on the move or conventional charger at home. Thats why I use a hybrid battery (eg Exide Extreme, Overlander or marine battery) as my auxillary.

yeah Dodge, I've heard about those diode boosters but am a bit reluctant at this stage until I've got my head around it.

That's what threw me. On the one hand, the alternator only has sufficient charge for the main battery yet this guy reckoned because I wasn't utilising the aux batt it just kept absorbing charge and was therefore overcharging. To be fair, he hadn't had a good look at it and suggested I book it in but he doesn't sound like he is across these issues. I think we get auto sparks that are decent enough in the general area but they often don't understand the applications.

Steve,
I very much doubt that your (and my) Prado with an alternator output at 13.1 to 13.4 could overcharge any lead-acid battery. More likely that a typical aux battery will always be undercharged to an extent, resulting in sulphation and reduced calendar life.

If I were you I' d go down the path of a dc-dc charger for your second battery. I think you will need to choose the battery and charger combination because not all dc-dc chargers can provide the ideal output for all batteries. A fully programmable one such as a Ranox (sadly, no longer avaiable) can. Most others have switch settings which are usually close to required settings but not bang-on, depending on the battery.

Choose a battery and dc-dc charger combo that will live happily together.

Cheers

thanks mate - pm sent

just when you begin to get you head around this stuff they move the bloody goal posts