Have to replace both batteries, help!

**Vern** · 21st October 2013, 05:20 PM

This is where Tim (drive safe) should chime in

**POD** · 21st October 2013, 08:37 PM

Originally Posted by Eevo

how many volts is your alternator putting out???
all my cars are 14.0 or slightly more

14.2 volts is about standard for a vehicle alternator charging voltage. Optima's website states something like 15 or 15.5 volts (can't remember precisely, my head is swimming with numbers today) is required to achieve full charge. So it would only get fully charged when plugged in to a battery charger. So it's all well and good to be able to discharge the battery to 50%, but if it is only 85% charged to start with, after a days driving, then the advantage of the deeper discharge is lost.
I'm beginning to see why some people are prepared to put up with the noise of a generator.

**Eevo** · 21st October 2013, 11:59 PM

Originally Posted by POD

Optima's website states something like 15 or 15.5 volts

Recommended Charging Information:

Alternator: 13.65 to 15.0 volts

imho, from experience of my optimas, you wont have a problem if your alternator is putting out 14.2 volts.

**Eeny** · 22nd October 2013, 04:55 AM

I recently went through the exercise of fitting an aux battery to my 110.
I had the luxury of being parked in the battery shop and test fitting various sizes (and capacities) under the passenger seat.

the Optima batteries fitted nicely, but as an aux battery their capacity is pretty limited - in fact any battery that fitted without the need for mods of the under seat compartment was smallish and as a result, limited in capacity. - ie, a size dependent thing, not brand.

In the end, I decided that to place an aux bat next to the starting bat, I'd have to find a new home for the jack etc. SO, I decided to have an aux battery connected to the isolator by Andersen plug on longish lead (taking account of cable dia and voltage drop). It can be shifted according to luggage changes, and dropped into the tinnie or in the camping area without hassles.

the battery shop owner suggested his view that going for value for money, safety in terms of tipping over, storage capacity and mobility, a 120 Ah AGM was the go. I think it was $300.

I am very happy with my decision = so versatile.

**roverrescue** · 22nd October 2013, 05:53 AM

POD,
I know that everyone will always suggest doing what they do as we all think we have the problem sorted!
And I am no different!!!!
In your post you mentioned "I have a 120-watt solar panel to keep things topped up"

Now, as I mentioned in a recent thread about dual batteries.
I also have a 130 tray back, I have monted a 120W panel on gas struts as a lift up side on the drivers side of the tray. It is plugged into a regulator which then charges directly into the battery box.
My battery box is simple, it contains a pair of N70 marines with a heavy cable between the positives.

No BS just simple bulk power for winching and running the fridge.
With the ute parked with drivers side facing north, the panel angled at about 45degrees
The batteries are fully charged by 930am with engel running at 0 degrees in the locked up cab (obviously full sun). This is up on the Cape in dry season where we get plenty of good sun, but if a 120W panel can keep the pair of batteries charged and running the engel indefinitiely I just cant see why you would do anything else!!!!

So mount you panel onto your fine loking tray lift panels, buy a pair of N70s Century MarinePro or whatever floats your boat and be done with it!!!!

Steve

**OffTrack** · 22nd October 2013, 05:59 AM

Originally Posted by POD

14.2 volts is about standard for a vehicle alternator charging voltage. Optima's website states something like 15 or 15.5 volts (can't remember precisely, my head is swimming with numbers today) is required to achieve full charge. So it would only get fully charged when plugged in to a battery charger. So it's all well and good to be able to discharge the battery to 50%, but if it is only 85% charged to start with, after a days driving, then the advantage of the deeper discharge is lost.
I'm beginning to see why some people are prepared to put up with the noise of a generator.

Have a look at the Optima specs again.

Alternator charging voltage for the D31 (75ah) is 13.65 - 15V at UNLIMITED amps

Battery charging voltage is 13.8 - 15V at 10 amps.

From 100% discharge/ 10.5V (which these batteries are designed to handle: OT add) charging time is:
100amps: 52 minutes
50 amps: 112 minutes
25 amps: 210 minutes

Recharge time will vary according to temperature and charger characteristics. When using Constant Voltage chargers, amperage will taper down as the battery becomes recharged. When amperage drops below 1 amp, the battery will be close to a full state of charge.

So the advantage of the Optima is that you can use most if not all of the capacity, and they are very fast to recharge from an alternator.

If you were looking at a 120Ah battery to discharge to 50% SOC you would have 60ah usable capacity. A 75Ah Optima discharged to 20% SOC gives you 60ah usable capacity.

If you are set on DC-DC charging have a look at the CTek Dual 250S/Smart Pass pair ( http://www.ctek.com/au/en/chargers/SMARTPASS , http://www.ctek.com/au/en/chargers/D250S%20DUAL ). With this setup the Smart Pass uses alternator charging to bulk charge because it is far faster than a DC-DC charger, then uses the DC-DC charger to top up and run a maintenance charge.

I personally use one of drivesafe's Traxide isolators and have been very happy with it so far. These have the advantage of sharing the starter and second battery down to 50% SOC then isolate the starter. This leaves the starter with ample charge to fire up any engine (there are many AULRO users with these isolators fitted). By splitting the load across two batteries you discharge each half as much meaning they recharge quicker - the alternator will charge both simultaneously.

cheers
Paul

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