Dual Batteries - JeepForum.com

 
LinkBack Thread Tools
post #1 of 9 Old 03-31-2010, 08:24 AM Thread Starter
TheGhost
Registered User
1983 CJ7 
 
Join Date: Feb 2010
Location: Tennessee
Posts: 120
Dual Batteries

Got a quick question that I'm sure someone like JeepHammer or Mike Romain will know the answer to. If I am running two batteries (12 volts) and one of the batteries starts to not be able to hold it's charge - will that hurt the other battery or cause it to discharge prematurely (the bad battery draining the good battery)? Does low voltage in one battery act as a load on the other battery?

TheGhost is offline  
Sponsored Links
Advertisement
 
post #2 of 9 Old 03-31-2010, 08:44 AM
jfwireless
Registered User
1976 CJ7 
 
Join Date: Apr 2007
Location: Naples, FL
Posts: 1,417
Quote:
Originally Posted by TheGhost View Post
Got a quick question that I'm sure someone like JeepHammer or Mike Romain will know the answer to. If I am running two batteries (12 volts) and one of the batteries starts to not be able to hold it's charge - will that hurt the other battery or cause it to discharge prematurely (the bad battery draining the good battery)? Does low voltage in one battery act as a load on the other battery?
Yes, a bad battery can impact a good battery if in parallel. Do some searches, JH has made serveral posts regarding dual battery set ups.

In general when batteries are in the permanent parallel mode they should be of the same type, size and, age.

Jim
jfwireless is offline  
post #3 of 9 Old 03-31-2010, 08:48 AM
Trapshooter
Registered User
1986 CJ7 
 
Join Date: Mar 2007
Location: Jacksonville, Oregon
Posts: 2,309
Depending on how your dual battery system is wired will determine whether the bad battery will drain the good battery.

'86 CJ7, 258, Carter BBD, Nutter'ed, TeamRush'ed, T-18, Twin Sticked Dana 300, D30 Frt-Pwr Lok L/S-4.10, AMC 20 Rear-Mosers-Detroit Locker-4.10, 2.5 BDS Lift, 1" Body Lift, 33" Wild Country M/Ts, Black Spoke wheels

'45 CJ2A, L134 Go Devil, T-90 Tranny, Warn O/D, T-18 T-Case, Dana 25 Frt, Dana 41 Rear, 531st CJ made

My 401 build: http://www.jeepforum.com/forum/f8/tr...build-1338277/
Trapshooter is offline  
post #4 of 9 Old 03-31-2010, 08:49 AM
BioTex
Registered User
2006 TJ Wrangler 
 
Join Date: May 2008
Location: Alpine, Tx.
Posts: 3,173
X2^

The weaker battery will impact the stronger one.

'85 CJ7, BDS 4" lift, 1" Body lift, 33x12.5, Shrockworks Sliders, 304 V8 with RV cam., T-176, D300, Dana 30, AMC 20.
1986 CJ10-A SD-33 Diesel/727/np208
1971 800B with 345/T-19
06' TJ Rubicon, 4" R.C. springs, BFG/AT 35s M.C. 6" fenders, rockers and surrounds, Currie front & rear adj. tracbars, tattons DC rear shaft, adj. upper - lower CA's. Bilstein 5100's
YJ Buggy Build Current project. Stroker/FI ?
1990 MJ Comanche 4.0L AX15/np231
BioTex is offline  
post #5 of 9 Old 03-31-2010, 08:49 AM Thread Starter
TheGhost
Registered User
1983 CJ7 
 
Join Date: Feb 2010
Location: Tennessee
Posts: 120
OK - Thanks. That's sort of what I thought - just looking for confirmation.
TheGhost is offline  
post #6 of 9 Old 03-31-2010, 08:50 AM
NC96XJ
Registered User
1997 XJ Cherokee 
 
Join Date: Jan 2010
Location: Kinston, NC
Posts: 43
^x3 does the same thing with golfcarts. best thing to do is get a battery switch then you have the option of running one or the other or both at the same time

96 xj 4.5" 33" cooper stt's bumpers roof rack
Built Not Bought #312
NC96XJ is offline  
post #7 of 9 Old 04-01-2010, 12:52 AM
Cutlass327
Web Wheeler
 
Cutlass327's Avatar
1978 CJ5 
 
Join Date: Jan 2009
Location: Beach City
Posts: 5,878
Semi trucks run 3 to 4 batteries, and if one developes a bad cell or whatever, it can take the other 3 down to where it needs jump started.

Rick

1978 CJ5 5.0HO/T177/D300, '86 D30/D44 WT axles, 'glass body, 31x10.5 BFG A/T, TDK galv'd frame - DD and weekend toy

http://www.jeepforum.com/forum/f8/ri...8-cj5-1223197/
Cutlass327 is offline  
post #8 of 9 Old 04-01-2010, 07:02 AM
JeepHammer
Running On Empty...
1973 CJ5 
 
Join Date: Aug 2007
Location: South West Indiana
Posts: 11,180
When a battery in a connected string goes bad,
It demands CONSTANT charging...
That will OVERCHARGE the rest of the string, and overcharging results in overheating and warped plates.
---------------------------------------------------

One way to avoid this is with a CHARGE ISOLATOR.

A charge isolator takes the current from the alternator,
And uses a voltage regulator for EACH BATTERY.
This DOES NOT work if you have the batteries wired together in a string...

In your case,
You would want to,

A. Fix the dead battery, probably replace BOTH at the same time with the same age, size, type of batteries,
And use the 'Good' battery in something else...

B. Replace the 'Bad' battery, and wire your batteries for 'Isolation'...
Which adds some wiring, but also gives you tremendous trail redundancy.
--------------------------------------------

If your batteries are wired directly together during operation,
(Even with a solenoid type 'Battery Isolator' that connects them together during operation)

You will want to replace BOTH batteries with the same size, type, age...

An 'Old' battery next to a new battery will cause the same issue, just slower to kill the new battery.
The older battery requires more charging, while the 'New' battery is getting cooked.

If you have a 'Staring' or 'Automotive' battery next to a 'Deep Cycle' battery, you should NOT connect them together except in emergency situations....
(Jump starting, winch operation, ect.)
'Deep Cycle' and 'Starting' batteries are built MUCH differently inside,
And charging the two together will cook one of them.

If you have two different sizes of batteries,
One a larger, higher output, and one a smaller, lower output battery,
You MUST use them isolated.
Again, one will demand more charge, and the one that doesn't need it will cook.
-----------------------------------------------

With a SECOND starter relay (Solenoid) on the fender, you will connect BOTH batteries to the starer when starting.
This gives you TWICE the starter amperage, and your starter will be VERY happy!

I actually had a starter relay quit working, and didn't even know it until I did maintinance/oil change and checked the starter relays individually, finding out one had given up as much as 3 months earlier!
The second starter relay started the vehicle without me even knowing one was not working! TRAIL REDUNDANCY!

This also keeps the batteries ISOLATED when not in heavy/emergency use.

Combined with a charge isolator if you have different size, age, type of batteries,
The batteries are NEVER connected together except when you are lugging with the starter.

A second set of winch relays will keep the batteries isolated until you do some winching, then BOTH batteries will help the winch work,
And go back to being isolated when you shut the winch off.

With a solenoid or manual connector switch between batteries,
You can 'Self Rescue',
Self jump start if the lights or radio gets left on,
You simply connect the two batteries together, and start the vehicle up to charge the dead one back up.

I once had the alternator quit about 20 minutes into a trail day at the local off road park...
That would have normally been the end to my day, and my $20 admission fee...
But I flipped the self rescue switch, both batteries worked together, and it shut off the 'Non Essential' items, like radio, air compressor, lights, ect.
And finished my day, picking up a common alternator and installing it on the way home. TRAIL REDUNDANCY!

It's extra wiring, which people run from like the plague,
But once you understand the principal, it's not hard to do at all.

Last edited by JeepHammer; 04-01-2010 at 07:23 AM.
JeepHammer is offline  
post #9 of 9 Old 04-01-2010, 08:44 AM Thread Starter
TheGhost
Registered User
1983 CJ7 
 
Join Date: Feb 2010
Location: Tennessee
Posts: 120
Thanks for all the insight. I think I'll move this down a bit on the list until I can get 2 new batteries and do it right. I found another JH thread that had the wiring diagrams - be not afraid...for I am Sparkacus!

Thanks to all who responded!
TheGhost is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.



Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Jeep Forums Replies Last Post
Guest Battery Selector Switch and dual batteries jatepper Jeep CJ Forum 8 11-23-2009 09:30 AM
My CJ eats batteries! sally77cj7 Jeep CJ Forum 26 04-04-2008 08:20 PM
Dual Batteries & H.P. Alternator 8679cjs Jeep CJ Forum 5 08-07-2007 11:46 PM
Dual batteries in 82 CJ FIRE1 Jeep CJ Forum 5 01-11-2007 01:57 PM
Dual Batteries CJ7Jeff Jeep CJ Forum 1 05-16-2002 10:26 AM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome