Dual Batteries - now I am really confused

Submitted: Sunday, Apr 04, 2004 at 09:26
ThreadID: 11809 Views:2510 Replies:9 FollowUps:19
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I read through all the posts on DB systems and I, knowing nothing about electricity except it hurts and might shorten your life, went off to find the best price and system for me. Mind you I did not understand half of the stuff in the posts. Confusion reigns on the web sites of all the major suppliers in that they each offer more than one system but really do not tell me what I need to know. What do I need. So off I go with Leonie to dealers to see what they say. I find it an excellent idea to take the wife on these expeditions as I generally end up buying nothing unless she is convinced it is the right thing. This is good because I can get so excited about these things I'm a pushover to the first salesman. Any way we only got to one dealer and I was stumped. My understanding is that you have one "normal" cranking battery and a "deep cycle" to run all the accessories. A winch is run off the "normal" battery. No! This dealer, who I do not doubt his competancy because he said I had a nice vehicle, said you have two "normal" batteries and run the accessories and winch off the second battery and have a switch to isolate the second battery when winching so you do not blow the alternator. (This means to me that having the engine running to assist the battery when winching will not work.) He says its better to have "normal" batteries because they charge up quicker. A deep cycle battery after a night running a fridge will take "a long time to recharge" but a normal battery will only take 1 hour and a half. He was selling Rotronics gear by the way.
Should I have my second battery a deep cycle or normal?
Should I run the winch off the crancking or second battery? or
not take the wife and just tell the dealer to do what they think is best because I know nothing.
PS the after burners are good for tailgaters.
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Reply By: Member - Errol (York WA) - Sunday, Apr 04, 2004 at 09:58

Sunday, Apr 04, 2004 at 09:58
Ga,day Richard . IMHO , two normal battery,s , run the winch off the crancking battery and everthing else off the second battery ( raidos , fridg , ect ) . Isolate the second batt so when useing the extras , you dont flatten your crancking batt . Thats my setup and it seems to work ok . Cheers .
AnswerID: 53129

Follow Up By: Richard & Leonie - Sunday, Apr 04, 2004 at 16:40

Sunday, Apr 04, 2004 at 16:40
Cheers Errol. Whose DB system do you use to link the batteries? By the way my wife thinks we need to get a life asking and answering questions on the forum but I told her looking at your setup you have the life. I agree about seeing Oz first.
FollowupID: 314896

Follow Up By: Roachie - Sunday, Apr 04, 2004 at 17:12

Sunday, Apr 04, 2004 at 17:12
G'day Richard & Leonie,
I agree with Errol 100%. I have numerous accesories all running off my second battery. I have used a deep cycle job and it goes well for a while initially, but after a few weeks on the road, I noticed that it wasn't charging up as well as it did when we first left home on a trip. After some investigation, I found that it wasn't getting enough charge during the day's driving to completely top it up for the next night's running of fridge, lights etc. So now it's 2 cranking batteries. My GU is 3.5 years old and still has the original starting battery after 118,000klm. The 2nd battery is now a Exide Extreme N70ZZ. I have a warn 9000lb winch and it is connected to the main battery. It doesn't get much use, so I don't believe it makes a great deal of difference which battery it's connected to. Just as a side note, I have installed a heavy duty in-line switch on the POSITIVE line to the winch in case any low life ties to crush my roof by hooking the cable to the tow bar and shorting out terminals on solenoid box.....just for kix.....mongrels.
Now to switches. I use a simple solenoid set-up. It is wired to my wiper motor as a "trigger". This means that the 2 batteries are electrically isolated as soon as the motor is turned off (ie: if the windscreen wipers won't work, the batteries are isolated). I could have left it at that, but also installed a switch in the cab. The purpose of this switch is to continue to have the 2 batteries isolated, even when I have the motor turned on. This can be useful if, for example, you have used the 2nd battery too much the night before and know that it is quite flat. If you don't have such a switch, then as soon as you turn the ignition on the 2 batteries will/may try to "equalise" (a bit like to tanks of water joined by a hose.......if one is full and the other empty, then when a tap is turned on between them (ignition), they will try to equalise). If this happens, you may find you do not have enough cranking power to start the engine, even though the starter battery was fairly fresh.
I've gone one step further and installed a voltmeter and yet another switch. Using this switch, I can swap between the 2 batteries to check what voltage is in each. Of course once the truck is running and I have switched the solenoid on, the voltmeter reads the same no matter which battery it is switched to read. So, before I start in the morning, I check to see how flat the 2nd battery is. If is down really low, I make doubly sure the solenoid is switched off.
The system I use is one you can very simply make yourself. However, it does not have any electronic components, & I don't know whether that could be a problem for a new vehicle with electronic black boxes etc.
I know it sounds complicated, but it really isn't.
I would like to steer you away from Deep Cycle batteries.....they are best suited to electric wheelchairs and the "go karts" used by the oldies.
(no disrespect meant to anybody).

FollowupID: 314903

Follow Up By: Gordon - Monday, Apr 05, 2004 at 13:49

Monday, Apr 05, 2004 at 13:49

Do yourself a favour and phone Rod Street at Rotronics in Brisbane. You will find he is a wealth of information.

I know he makes them and it is in his interest that you buy his brand, but I can guarantee that any question you can think to ask will get an honest response.

No, I don't work for them, just a satisfied customer.

FollowupID: 314968

Follow Up By: Member - Errol (York WA) - Monday, Apr 05, 2004 at 14:33

Monday, Apr 05, 2004 at 14:33
I just went to the local auto lecke and bought the isolater from him , told him what i was going to use it for soas he knew what i needed . You could get him to hook it up for you if you want , that way you will know it will be dun properaly . Errol
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Follow Up By: Member - Errol (York WA) - Monday, Apr 05, 2004 at 14:38

Monday, Apr 05, 2004 at 14:38
PS . Also a good idea to run a power wire from the isolater to a fuse box and have all wires to raidos and any other extras going out from there . That way , all the fuse,s are in one spot .
FollowupID: 314971

Follow Up By: Member - Errol (York WA) - Monday, Apr 05, 2004 at 17:49

Monday, Apr 05, 2004 at 17:49
Sorry Richard . I ment the battery , not the isolater .
FollowupID: 314994

Reply By: Brad - Sunday, Apr 04, 2004 at 10:08

Sunday, Apr 04, 2004 at 10:08
Agree totally with Errol.
'Normal' cranking batteries are cheap enough that they can endure a couple of years of the abuse we give them ( eg storing them in a hot environment, variably discharge and then incompletely recharge etc) and then replace. You probably wouldn't feel like doing that to true deep cycle $500+ batteries.
I have another auxiliary battery in the camper, so I aim to buy one new 'cranking' battery each 12-18 mths, which will go in the starting role, next best as the 4wd auxiliary,3rd best into the camper and the 3-4 year old one gets ditched.
AnswerID: 53130

Follow Up By: Richard & Leonie - Sunday, Apr 04, 2004 at 16:42

Sunday, Apr 04, 2004 at 16:42
Thanks for taking the trouble to answer the questions. What DB system do you use?
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Follow Up By: Brad - Sunday, Apr 04, 2004 at 17:28

Sunday, Apr 04, 2004 at 17:28
ARB installed their 'smart solenoid'. I know very little about electrics either, so my only comment is the system has been faultless,everything works all the time ( we do tend to drive almost everyday, and at least every second day on a trip, so the system gets plenty of charging compared to someone who might put their feet up in one spot for several days).
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Reply By: Dave from Fraser Coast 4WD Club - Sunday, Apr 04, 2004 at 10:09

Sunday, Apr 04, 2004 at 10:09
for me, I use two 'hybrid' batteries, ie Exide Extremes, less CCA than a normal starter, but greater Ah.

I have found these to be very good for my application.

The dealer was right about DC taking longer to charge, but he should have added the word "properly" Amps is Amps, but different types of batteries accept them differently.

As for the winch, i'd always believed that you need the input from the alternator, or better yet get a hydraulic one!!

For a basic DB (read idiot proof) system try the TJM XGS, (we have these on work vehicles).
AnswerID: 53131

Follow Up By: Richard & Leonie - Sunday, Apr 04, 2004 at 16:55

Sunday, Apr 04, 2004 at 16:55
Cheers. I have just fitted an Exide Extreme as my first battery. We are heading for the Cape and although the original Delco battery was only 2 years old and working OK I thought it safer to start off on a three month trip with a new quality battery. From what everyone has said todate I can move my old battery on to be my second battery. Thanks for the info on the DB system you use. I have previously been onto TJM's web site and although it has two systems shown (I think they are two different systems) it does not really tell me what the differences are and what I need. I have emailed them for more info but on their past performance of not answering emails I shall not hold my breath for an answer. I thought I might set up a business of checking company web sites to see if they are user (read useless) friendly on the information supplied.
FollowupID: 314898

Reply By: Eric from Cape York Connections - Sunday, Apr 04, 2004 at 12:59

Sunday, Apr 04, 2004 at 12:59
Richard I think like you get the professionals to fit it let them know what you intend to use it for. Then tell she who must be obeyed we need it and it will make her life easier when were away and take her out for dinner and flowers and hopefully the darlings ok it.

All the best
AnswerID: 53142

Follow Up By: Richard & Leonie - Sunday, Apr 04, 2004 at 17:00

Sunday, Apr 04, 2004 at 17:00
Well you can tell Peter he can suck up to my wife when we see you later in June.
FollowupID: 314899

Reply By: Willem - Sunday, Apr 04, 2004 at 13:59

Sunday, Apr 04, 2004 at 13:59

It becomes like one of those school questions....If I had six eggs and three chickens and four apple scraps and I take away three boxes then how many laying pellets would I have left ????

I am also a novice at the battery thing but I managed to rig up my own system.

Starting battery is a 700CCA cranking battery and the winch cable is attached to it as well. So when I am winching the alternator can charge the battery if the engine is running on higher revs. Auxilliary battery is also a cranking battery of 700CCA(an old one) and I run all the extras off it including the fridge. I fitted a Rotronics MH10 battery isolator in between the two batteries according to the instructions in their booklet. NOTE: Rotronics do not supply cables to hook the batteries up to each other via the unit and wanted $70 for them. I used jumper cables at $10 a pair. Everything works very well. Easy............But there are issues with more modern vehicles with spiking(dunno what that is) and other stuff...no worries with my old truck though.

Cost: Rotronics MH10 $260
Addtional battery $125
Jumper cables $ 10
Installation..self 0
Total $395

AnswerID: 53145

Follow Up By: Member - Eskimo - Sunday, Apr 04, 2004 at 17:01

Sunday, Apr 04, 2004 at 17:01
willem, Spiking is a term used to indicate that a high voltage "spike" has blown up the onboard engine management system. Similar to what happens when you open or close a switch on high voltage eqipment and a back EMF occurs or something like this anyhow haha

I am not convinced it happens if a battery is in circuit as batteries are supposed to act as a big soak "smoothes out the spike"
FollowupID: 314901

Follow Up By: Richard & Leonie - Sunday, Apr 04, 2004 at 17:11

Sunday, Apr 04, 2004 at 17:11
Willem, thanks for taking the trouble to reply. See my wifes comments above in Errols follow-up. The Rotronics systems appear simple enough and the installation info given seems pretty comprehensive. The use of jumper leads to connect seems a good idea particularly if the distence between the batteries is large. With my proposed set up one battery is at the front driver side and the second would be at the firewall on the passenger side.
By the way I hope I understand you correctly when you say you connect the winch cable to the battery. You do mean the electrical wires don't you? Yes, I know but it just sounds funny.
Don't worry, Be happy. I agree. Jolley by name and Jolley by nature, thats me.
FollowupID: 314902

Follow Up By: Roachie - Sunday, Apr 04, 2004 at 17:22

Sunday, Apr 04, 2004 at 17:22
I thought I'd just throw another 2 cents worth in when I read Willem's ideas. I'm not trying to be a smart-ar*e..........
Willem said he connected the 2 batteries using jumper cables. I'm assuming that what he meant to add was that he simply bought the cables, but that he cut off the large aligator clamps and soldered on a proper lug at each end. You said you were a complete novice and I wouldn't like to think that you would just chuck a jumper lead under the bonnet clamped to the terminals......
FollowupID: 314904

Follow Up By: Willem - Sunday, Apr 04, 2004 at 19:38

Sunday, Apr 04, 2004 at 19:38

Yes .....I should have said....Electrical cable


Yes, I cut the the jumper clamps off and fitted proper cable ends to the jumper cables. Didn't exactly solder them but cleared enough wire and used a sledge to reshape the cable ends on to the wire. It won't move in a 1000 years.


Thanks for the explanation. The only onboard managemt system in my truck is my right foot....hahahahahaha

FollowupID: 314912

Follow Up By: Member - Cocka - Sunday, Apr 04, 2004 at 19:48

Sunday, Apr 04, 2004 at 19:48
My setup is pretty much the same as Willems without the winch. Rotronics are very approachable and gave me a good setup for my needs. Re the battery leads, the idea is that you carry a set as you always would but if you have to jump start the cranking battery then you do it from the aux bat using the leads. I have never had to use them, touch wood.
Willem you can buy heavy weight jump leads with resistor diods in them that protect on board computers from power surges. Without meaning to be unkind I'm not sure that this is a problem for your wagon.
I also fitted a monitoring system from Rotronics to keep an eye on the oil pressure and water temp. If either system move from the normal settings an audible alarm sounds, it gives great peace of mind and saves having to scan the dials every 5 minutes.
FollowupID: 314917

Reply By: Rosscoe - Monday, Apr 05, 2004 at 10:27

Monday, Apr 05, 2004 at 10:27
Some "light" reading, if you are interested;-


The type of battery depends largely on its intended use.

Either way, from my understanding, neither battery is happy being fully discharged or even discharged regularly below 40%. Shortens their life dramatically.

Also neither type of battery can be 100% carged from a standard vehicle/voltage regulator system. Conservative estimates suggest a maximum of 80% although some say you're doing well at 70%.

Result is typically you only have 30 to 40% of battery's rated capacity for use. ie an 100 AH battery allows a maximum of about 40 AH or enough to run a typical 12V fluro (which draws 1 amp) for a period of 40 hours continuous.
AnswerID: 53220

Follow Up By: Richard & Leonie - Saturday, Apr 24, 2004 at 21:40

Saturday, Apr 24, 2004 at 21:40
Do they come in other colours? Needless to say my understanding about charging is the same so does this mean that someone needs to come onto the market with a charging system that will fully charge a battery.
Sorry for the delay in answering, we've been away. Oh the joys of being retired.
FollowupID: 317651

Follow Up By: Rosscoe - Tuesday, Apr 27, 2004 at 09:50

Tuesday, Apr 27, 2004 at 09:50
There are devices which will fully charge your batteries.
240V ac mains operated "Multi-stage smart chargers" cost about $300.00 and much more for the flex that trails for thousands of kms behind your vehicle!
Petrol motor driven alternators BUT they can "cook" your battery if not monitored closely.
Solid state devices like the ARRID twin charge unit for mounting in the trailer/caravan, "claim" to fully charge the battery from the vehicle electrical system. I'm still investigating these.
Finally and probably the best is a "correctly" sized solar system and "proper" solar regulator. My estimates for a system that I want is upwards of $1,000.00 probably more like $1,200.00.
IMO deep cycle batteries are right for me. BUT like all lead acid batteries, discharging them below 40% of charge dramatically reduces their life. Storing them at low charge level also causes sulphation of the plates and also shortens their life.
They handle regular charge/discharge cycles well provided you observe the above.
Two good books on the subject have been written by Colyn Rivers of caravan and Motor Home books.
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Reply By: -OzyGuy- - Wednesday, Apr 07, 2004 at 20:07

Wednesday, Apr 07, 2004 at 20:07
Richard and Leonie,
I have read the replies here and my comments are totally different to them, more in tune with your own understanding of Batteries and Isolators.
Yes, you definately do run your winch off the Crank battery where you can give it extra power from the altinator as required....

I run 2 x Delkor 80 Amp Hour Deep Cycle batteries with a 80 Watt Solar panel seperated from the start battery by an Electronic Pirahna Isolator. I spend months at a time camped on the beachs in the North West of West Australia, so I have to have a totally reliable power system, as I dont have to start the vehicle to recharge batteries at all. I only go into town once a week. Deep Cycle batteries are designed to be 'cycled' constantly...

When you read the various Battery makers specifications you will understand better the reasons they give why Deep Cycle batteries are chosen to run fridges etc.

Enjoy your travels......
AnswerID: 53601

Follow Up By: Richard & Leonie - Saturday, Apr 24, 2004 at 21:30

Saturday, Apr 24, 2004 at 21:30
Thanks for your input. Sorry to take so long to get back to you. I have been away. I think I will go for the deep cycle battery as the second battery. I can only get an 8 inch long battery in so I cannot recycle my cranking battery as suggested by others, even though it sounds a good idea. The deep cycle batteries I understand can be discharged more and more often without damage and as it will be a small capacity this is important. I like the idea of the solar power charging but at present I think if I load anymore stuff into the Frontera the wheels will go horizontal. I put it over a weigh bridge fully loaded for camping with 55l of water and 170 litres of fuel, me and the misses and it weighed 2.45 tonnes. I have uprated the suspension and even with that weight in it only went down 10mm. Still, what panels do you use, how big are they and what do the weigh. I went to the sydney camping and caravan show today and it seems to me the solar panels are on the up as far as availability is concerned.
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Reply By: -OzyGuy- - Tuesday, Apr 27, 2004 at 22:39

Tuesday, Apr 27, 2004 at 22:39
I use a Solarex 80 watt panel, it is 65cm wide x 110cm long
as to what it weighs, well I dont know for a fact, however the 4 x sides are aluminium chanel so you could say maybe only a couple of kilo's and the actual panel would only weigh a few kilo's max - I think.
AnswerID: 56306

Follow Up By: Richard & Leonie - Wednesday, Apr 28, 2004 at 15:13

Wednesday, Apr 28, 2004 at 15:13
Thanks. Thats useful info. At that size it would fit nicely inside the car between the top of my rack system and the roof.
FollowupID: 318134

Reply By: TJ - Monday, May 03, 2004 at 15:27

Monday, May 03, 2004 at 15:27
Richard & Leonie,

Hi, I did an installation myself with a solenoid from ARB and their Battery Tray. The Cables I had made up from Battery World. The only suggestion I would like to make is that you have a look at using a marine battery as your second battery. It appears to be something of a crossbread, part deep cycle and part normal. Like most of these things they end up being horses for courses, what suits your needs.

Good luck

AnswerID: 57021

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