dual battery AGAIN!

hi to all,
has anyone charged two different batteries together.
i have a 115ah commander d/cycle marine and a spare h/duty cranking battery.Both are wet cell.
I have learnt that one must use the SAME batteries when charging them together.
What actually happens?does the d/cycle batt.suffer from not charging as fast as the cranking battery?
Note ,i am not using the in car cranking battery.
I wish to charge the two from my 120watt solar panels through my controller which works great [lots of power on clear days.]
the 115ah d/cycle isnt holding out long enough on long camps with cloudy days on its own.
i let the deep cycle charge by the sun when travelling as i have a fused 6mm double insulated wire running the fridge full bore from the car cranking battery when driving.
I cannot afford to buy another 115ah batt. or set up to charge from the alternator ,battery etc.
SO the question is ,what is the problem charging two different wet cell batts.
thanks to you all for the information i have gleaned to set up this rig.
happy and safe travells to you all.
Regards Roger P

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Reply By: Bryan (WA) - Thursday, Apr 02, 2009 at 13:31

Thursday, Apr 02, 2009 at 13:31
Hi Roger,
it is highly recommended the betteries are the same - but in reality its not going to happen when you have to mix starting and deep cycle batteries together for different purposes - camping.
I have a starting battery for the engine only and then run the fridge from my fully sealed deep cycle batteries (I use Hawker energy SBS60 batteries and depending how long we are away I will use 2 or 3 in parrellel to give me eaither 120 or 180Ah or capacity). 2 of these batteries in parrellel will run my 50L waeco for over 4 days without any recharging and Im still not at the low voltage cut over setting at 10.2v. When we are travelling I then let the alternator charge them. The batteries are protected by a battery box to protect them/us incase of any damage.
when at home I keep them connected to the smart charge which is fitted in our Camprite camper to ensure they are kept charged and in good condition.
I ran 8mm core cable from the front of the car to the batteries in the back of the Patrol and used cct breakers for short cct protection, and interconnect the batteries with 10mm core cable.
I think you will find everyone has slightly different setups to suit their needs. mine is certianly far from perfect.

hope this helps.
AnswerID: 357666

Follow Up By: Bryan (WA) - Thursday, Apr 02, 2009 at 13:38

Thursday, Apr 02, 2009 at 13:38
Opps slight error - my starting battery powers the car as normal. the deep cycle batteries only power the fridge and are only connected to the car 12v system when charging them.

FollowupID: 625770

Reply By: greybeard - Thursday, Apr 02, 2009 at 13:38

Thursday, Apr 02, 2009 at 13:38
interesting read.
isolating batteries
note the references to external sources.
AnswerID: 357667

Follow Up By: Member - Norm C (QLD) - Thursday, Apr 02, 2009 at 14:39

Thursday, Apr 02, 2009 at 14:39
Thanks for that link Greybeard. I've seen some of this info before, but not all of it.

I've been paralleling different batteries for years. Many people have such fixed and outdated view on this however, that I generally don't bother to debate the issue any more. I just do what I do.

After all most of us parallel starter and deep cycle batteries for charging (that's what isolators do). And many of these same isolators leave them paralleled during discharge until the voltage drops to a pre determined level.

Norm C
FollowupID: 625780

Reply By: Peter_n_Margaret - Thursday, Apr 02, 2009 at 13:41

Thursday, Apr 02, 2009 at 13:41
Roger, provided the recomended charging voltages are similar for both, then no problem.
Alternators Vs are often a bit low to get full charge into some battery types. The float setting on the solar controller might be a bit high for some batteries.
Since they are both wet cells, you are probably OK, but check the manufacturers recommendations and the actual voltages of your charger/controllers.

I am using a two way Redarc between my crank (calcium) and house (AGMs). The alternator is 14.3V and the solar PL controller is the same. This way, my solar also tops up the crank when the house is full. Not quite your question, but in the same paddock?

OKA196 Motorhome
AnswerID: 357669

Follow Up By: roger p - Thursday, Apr 02, 2009 at 18:20

Thursday, Apr 02, 2009 at 18:20
thanks peter n marg,
did check float settings,at 14.8.[on controller]
desulphure mode pumps up to 15.something.[for 2hrs ]monthly.
am hoping the two batteries will give me ample power.
my spare i wiill try is a supercharge ns70, 585 cca130mins rc.
it might work a while.[with the 115h batt.]
cheers roger
FollowupID: 625812

Reply By: roger p - Thursday, Apr 02, 2009 at 14:34

Thursday, Apr 02, 2009 at 14:34
to brian,
thanks for your input,sounds a good setup you have.I am being "tight"as times are tough and i will be bush camping almost 7 months.I dont want to spend excessive money and rely on the cranking battery when i will be stopped weeks at a time.
If i buy another 115ah battery i will have more than enough energy in store,need fish frozen an beer cold.
just had a squizz at greybeards article[thanks] and will study it further.confusion still reigns.
Peter i might give the two batts. a go and take seperate readings at intervals to see whats doing.
When the sun shines again that is ,overcast and wet the last 5 days here in the hunter valley.
May have to leave something else behind and throw the genny in after all.

thanks guys Roger P
AnswerID: 357674

Follow Up By: Bryan (WA) - Thursday, Apr 02, 2009 at 15:23

Thursday, Apr 02, 2009 at 15:23
Hi Roger.
I have also set my system up on the low cost model....
I keep my cranking battery and the deep cycle batteries isolated by a 70amp relay I control manually. so i only ever allow the deep cycle batteries to conenct to the cars 12v system when we are driving and I know the main battery is full (I have a 100Amp Ammeter installed so I know exactly what is happening and to ensure I know if the alternator fails)..
I also have a digital volt meter I bought which monitors the battery voltage level at all times. this is what I bought for your reference:
I actually have 2 - 1 for monitoring the fridge batteries and the other for the battery in the camper trailer.

FollowupID: 625786

Follow Up By: Bryan (WA) - Thursday, Apr 02, 2009 at 15:27

Thursday, Apr 02, 2009 at 15:27
also you care about the volatge readings when the fridge compressor is running so you get the correct load voltage reading. if you measuer the voltage when the fridge is off, you will get the float voltage - which will give you a higher reading.
FollowupID: 625788

Reply By: Peter_n_Margaret - Thursday, Apr 02, 2009 at 16:13

Thursday, Apr 02, 2009 at 16:13
My son has a set-up that is budget AND different.
He has NO isolators and uses both of his DC batteries for both house AND cranking (in parallel).
Risky you ask?
No problem. All of the accessories (incuding lights and fridge) are run via low voltage cut-outs. This lets him use about 50% of both batteries (double that available if they were isolated) before the fridge etc gets turned off automatically. At that point, there is still plenty of grunt left to start the engine.
He also has a couple of solar panels to poke power in when camped.
This is all on an FJ40 shorty. Works well.

OKA196 Motorhome
AnswerID: 357684

Reply By: roger p - Thursday, Apr 02, 2009 at 16:36

Thursday, Apr 02, 2009 at 16:36
thanks you guys,
I have the low v cutouts sorted and as i aint using main cranking batt in system have that as reserve at all times anyway.
It cost me 50.00 last year for a jump start[from fellow nomads] for my xt falcon, towing a camper trailer at clem walton park 65km east of mt isa, after a few nights ,cd player and m/phone charging flattened the batt.so no start- till these others came along.
Any way i will be much wiser after this next 7 months,great to have MUCH sunshine up north in winter.See u all there!!!nd will let you know how it goes.
cheers Roger
checking out sidewinder site now.
AnswerID: 357689

Follow Up By: kevanancy - Thursday, Apr 02, 2009 at 17:51

Thursday, Apr 02, 2009 at 17:51
Very sad that a fellow traveller would charge you $50 for a jumpstart . Hope Kharma gets them .
FollowupID: 625808

Follow Up By: Leroy - Friday, Apr 03, 2009 at 10:03

Friday, Apr 03, 2009 at 10:03
Gee charging some $50 is a bit ruggered!!!

I wouldn't take payment by way of a slab of XXXX for helping out a German guy and his mum on Fraser. She was so offended that I wouldn't accept it lol. In the end I took a 6 pack to appease her. Also I didn't want to leave them with no beer!

FollowupID: 625925

Reply By: roger p - Thursday, Apr 02, 2009 at 18:06

Thursday, Apr 02, 2009 at 18:06
hi kevanancy,
hope thats spelt write.nice of you to reply.
I think those people may have been doin it a bit tougher than me in their 4wds and vans and i was keen on a start. with a solar panel ,at least i would have had a free charge in a couple of hrs hey.
i am not like that either,to expect $ for a hand on the road.a beer or cold drink helps start a conversation that leads to information money doesnt buy.
take care roger p

AnswerID: 357702

Reply By: drivesafe - Thursday, Apr 02, 2009 at 22:28

Thursday, Apr 02, 2009 at 22:28
Hi Roger p, the stories about not being able to have dissimilar batteries connected in parallel is nothing more than a myth.

If you were to have two identical batteries, one your cranker and the other your auxiliary, you are going to continually have a situation where the batteries are going to be at different states of charge when you connect them together in a parallel set up, how does this differ from have two dissimilar batteries being connected in parallel.

As stated, this is nothing more than a myth based on a misunderstanding. People continually mix up the requirements for connecting batteries in parallel with what is required when connecting batteries in series.

When connecting batteries in series, you MUST use the same type and size batteries otherwise one of them will never be fully charged and will have a shortened life span.

No such thing occurs when connecting dissimilar batteries in a parallel set up, tens of thousands of RV uses have been doing it for decades and don’t have any problems.
AnswerID: 357752

Follow Up By: Member - Mike DID - Friday, Apr 03, 2009 at 09:22

Friday, Apr 03, 2009 at 09:22
. . . and the other factor people forget about is that as soon as you install a Battery ISOLATOR, the batteries are no longer being discharged in parallel anyway !!!!

Hopefully this "batteries must be identical" myth will disappear (You'd be wasting money just buying a second battery, you need to buy TWO identical batteries off me, because we all know . . . )

Along with the "Alternators can never charge above 70%" myth (you really should but my expensive charging regulator, because we all know . . . )
FollowupID: 625903

Follow Up By: drivesafe - Friday, Apr 03, 2009 at 09:43

Friday, Apr 03, 2009 at 09:43
Hi Mike, in my case, I actually go further in that my controllers not only charge dissimilar batteries in parallel but keep the batteries paralleled while discharging and after supplying these controllers for more than 20 years and with tens of thousands of happy customers out there, I have NEVER had one of them have a problem associated with using dissimilar batteries.

Unfortunately, this myth and as you posted, the one about an alternator supposedly not being able to fully charge a battery, are going to continue to appear while there are unscrupulous individuals out there, who can make a buck out trying to get people to believe these two myths are fact.
FollowupID: 625912

Reply By: roger p - Friday, Apr 03, 2009 at 08:50

Friday, Apr 03, 2009 at 08:50
thats what i wanted to hear and will set it up today and give it a trial for a bit before i leave.
takes a LOT of home work when one starts from scratch.
This site is a veritable encyclopedia of information.Working out what is best for ones own use is the head scratchin bit.
thanks for that info.
cheers Roger
AnswerID: 357797

Follow Up By: drivesafe - Friday, Apr 03, 2009 at 09:44

Friday, Apr 03, 2009 at 09:44
Hi Roger, keep us informed on how you go.
FollowupID: 625915

Follow Up By: roger p - Thursday, Apr 09, 2009 at 08:29

Thursday, Apr 09, 2009 at 08:29
hello to all. refer to my opening thread.
i paralleled my 115ah and h/duty car battery to charge together [not cranking batt]and found that the h/duty battery was cooking and the deep cycle battery was staying undercharged,it wouldnt run my 70lt f/freezer for more than an hour before cutout.
Have gone back to the one d/cycle and fitted a dual batt isolator to charge while driving,will switch over to solar when stopped and take a genny and charger.
if i cant keep the freezer running on overcast days,so be it.Sick of worrying, take the b#@@#y genny and be done with it,if i have to run it i will.
Wish every one a great easter and safe travells.
roger p
FollowupID: 626912

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