Necessity of Dual Batteries

[doug720]

For years I went with dual batteries now I run dual batteries wire together in parallel with no controls or expensive dual battery systems and carry an antigravity jump bag. Twice the available capacity as your standard dual battery set up with the back up of a small jump bag. Now with drawing from both batteries at the same time I get much lower over nite discharges and my expensive batteries should last much longer.

I run the same set up. and it works great. If you have dual batteries, with or without an isolater, if one goes bad, both need to be changed out at the same time. If you buy 2 batteries at the same time for the vehicle, in my experience, they will warranty them both if one goes bad. I have had this happen in my650 and my diesel van in the last couple of months. Both AutoZone and Sears were no problem.

 

[titanpat57]

This was the guide I used...pretty elementary, but so far so good.

http://www.expeditionportal.com/for...ke-a-cheap-isolated-dual-battery-setup-for-50

Here was my install over on T4R.org

http://www.toyota-4runner.org/5th-gen-t4rs/125772-dual-batteries-cheap.html

So far to date there has been no issues or blown fuses, even during a few good pulls....and thanks to some help and guidance here for some pretty smart members, I have a new NoCo battery charge system to keep them completely topped off.

 

[atomicshawn]

...If you have dual batteries, with or without an isolater, if one goes bad, both need to be changed out at the same time...

While I can understand how a bad battery could stress a charging system, including the secondary battery, I don't get the "need" to replace both batteries if one fails and the other still tests healthy. Could you explain this further?

On a side note, it's been seven months now since swapping out the bad Odyssey for the Interstate... weeks of sitting around, several trips off road... and no problems so far.

 

[george_tlc]

While I can understand how a bad battery could stress a charging system, including the secondary battery, I don't get the "need" to replace both batteries if one fails and the other still tests healthy. Could you explain this further?

In a vehicle, with an isolated system where the dual batteries are only connected during charging (or jump starting etc), there is *NO* need to change both batteries with the "same type" and/or at the "same time".

cheers,
george.

 

[atomicshawn]

Yeah, based on my understanding and experience with batteries and charging systems, George you're opinion is mine as well. Just wondering what Doug720 is basing his ideas on.

 

[doug720]

It's not that replacing only the bad battery won't work; it's the fact that the old battery will pull the new battery down to somewhere slightly above it's own level. They WILL seek equilibrium with each other. This is not good IMHO, and most battery manufacturers say to replace in pairs.

Kind of like mixing old and new battery's in a TV remote, they run down faster due to them trying to find equilibrium.

Likely if one of the pair is bad, it made the "Good" battery work harder, be drained lower, and to be charged at higher rates. None is good, particularly for a starting battery.

Most battery dealers and manufacturers will swap both battery's if one goes bad in a dual set up.

Why not start fresh with both new?

 

[george_tlc]

It's not that replacing only the bad battery won't work; it's the fact that the old battery will pull the new battery down to somewhere slightly above it's own level. They WILL seek equilibrium with each other. This is not good IMHO, and most battery manufacturers say to replace in pairs.

Kind of like mixing old and new battery's in a TV remote, they run down faster due to them trying to find equilibrium.

Likely if one of the pair is bad, it made the "Good" battery work harder, be drained lower, and to be charged at higher rates. None is good, particularly for a starting battery.

Most battery dealers and manufacturers will swap both battery's if one goes bad in a dual set up.

Why not start fresh with both new?

Ah, the old myth of an old battery pulling down a new battery and equilibrium etc with an isolated system. This is *NOT* applicable where you have an isolated system where the batteries ONLY combine when the alternator is running.

SLA/Gell/AGM etc etc all charge with constant voltage charging (with various bulk/float etc stages). The alternator only sees the battery voltage and the battery only cares about the battery voltage (obviously with some sort of current limit) so if you have a new/old in parallel during charging there is no issue.

Your example of a TV remote is *NOT* applicable to this discussion since those cells are in SERIES.

Yes, with SERIES batteries (24V vehicle system) you DO want to replace both batteries at the same time and with the same type/model of battery as a matched pair.

cheers,
george.

 

[rusty_tlc]

This might illustrate what George is saying. I have had RV's for many years. If the battery in my truck goes bad I do not change the battery in my RV. This exactly the same system George is talking about, the only time the batteries combine is when the trailer is hooked to the truck AND the ignition is on.

IMHO the only safe way to set up a dual battery system is exactly like an RV system. The only shared connection should be with the alternator and that connection should isolate the two batteries through a relay (mechanical or solid state if that floats your boat).

 

[lugueto]

A few months ago I was thinking about doing my dual battery setup. Leaving the standard one alone and having the second one as a house battery (and a backup one, off course)

For a few reasons, I decided not to install the second battery and leave the vehicle as is. I always thought about the situations where I would need it, but I recently found my solution.

All my life I've carried a small generator to light up camp at night and for when I need electricity. A few years ago, I switched to power inverters for these duties. Since then I was forced to monitor the vehicle because I had the one battery, which was the reason for considering the dual setup in the first place.

In December, while on a trip, I decided to take my generator with me to get it running again. I discovered (I'm shocked I didn't before) that all generators have a 12V outlet, purposely made for charging batteries. This meant that, if by some reason my battery was dead, I could charge it anywhere. During that trip we charged a couple of vehicles that had fridges running 24/7 without a hassle and in under an hour. I haven't done it with mine yet but I do have the peace of mind that it is there when I need it, which was the feeling I was looking for when I first thought of the second battery..

 

[george_tlc]

Most generators output less than 10A on the 12V output, so charging a flat battery could 'take a while'... Charging enough to start the vehicle will take less time. A failed battery (dead cell) will still be bad news though...

I've camped with folk that take an AC based battery charger along and power it from the AC output of the generator. That way they can charge at 40A or more (depending on the battery charger) versus the more limited DC output of the generator.

Anyhow, lots of choices/opinions on a 2nd battery, how to wire it and other jump start options. Do what you feel works for your intended use.


I personally prefer a 2nd battery and solar to topping things up when camped (fridge, lighting etc).

I was on one trip when a friend's vehicle had a total battery failure (no 2nd battery in their vehicle). I removed one battery from our 80 and installed it into their vehicle so we could complete the trip and return to a town to purchase a new battery.

cheers,
george.

 

[atomicshawn]

I appreciate the generator idea brought up again. And while I can see the utility of a generator if you're running a fridge, extra lighting, etc... (I recall seeing a picture posted on Wasatch Cruisers that look like the group put on a rock concert out on the trail complete with electric guitars, mics, amps, speakers, etc...), I run kinda old school with a Yeti and a couple old Coleman propane lanterns (and an acoustic guitar and fiddle for the entertainment; ) so no big electrical demand. A generator doesn't really make sense for me. And if for no other reason, again, a generator can do little if the battery won't hold a charge.

BUT, it made me reconsider the charging system. If the alternator fails, and both batteries discharge, I'm back to granola.

I've wanted to pick up a set of brushes to throw in the bag, but I keep putting it off. I'm going to get it done this week...

 

[Cruiserdrew]

I hate generators. Noisy, smelly and not cool if you're running one and everyone else wants peace and quiet. They have no place in a 4wd rig where the goal is to explore the back country. If you need to run a generator, stay in a camp ground.

Dual isolated batteries basically eliminate the need, and solar is a good supplement to keep batteries topped off without being intrusive.

 

[atomicshawn]

I hate generators. Noisy, smelly and not cool if you're running one and everyone else wants peace and quiet. They have no place in a 4wd rig where the goal is to explore the back country. If you need to run a generator, stay in a camp ground...

lol! I was trying to keep an open mind, but well said!

 

[doug720]

There is differences between "Dual" batteries systems:

1) Dual batteries in parallel where both batteries are the same type and size and used to run the vehicle without an isolater


2) Dual batteries with an isolater where one runs the vehicle and one is for non vehicle accessories.

In option 1, replacing both batteries at the same time is the proper method. In option 2, the they are not directly tied together, so replacement would be the bad one only.

I have option 1 in my 60.


In our RV we have 8 6volt house batteries and one 12 volt vehicle battery. There is no reason to replace the house batteries if you replace the vehicle battery. But, in my experience, mixing old and new batteries in the bank does not work well. If all the bank batteries are a year or two old, not too many issues replacing a battery or two. But after that, we have always lost capacity. This may be due to all the batteries being several years old. But large banks like to be equal.

We have been fortunate and I take good care of our batteries, so we have had few issues with the RV house banks. Ours is charged by a high amp smart charger and 1000 watt solar array. We can camp for at least a week in limited sun - forest, and near limitless in open areas.

Our main bank is over 7 years old and I just replaced the starting battery last year after 13 years. Good batteries, distilled water, checked regularly and a good charger, keeps them alive.

As was mentioned, generators 12 volt charging is poor, so a good high amp charger is needed.

 

[Greg_B]

Phil,
so if you have your 2 batteries permanently wired in parallel, how do you know when one has died?

cheers,
george.

Even prior to dieing your combined voltage will read low giving you a heads up

I've not been running my 80 much lately and have had it at the shop with a Deltran Battery Tender Plus hooked up all the time. Batteries hooked up full time in parallel. Every time I pop by the shop I check the batteries. Through the summer I noticed it was in charge mode more then I thought it should be (no loads). A week ago when I went to install an awning it was in storage mode. Started and moved the vehicle and when done I put it back, with the charger hooked up. Stopped by the other day and noticed the charger was smok'n hot and the batteries were at 12.50(ish). I asked my shop mate to keep an eye on it till he left and disco it if still the same. Couple hours later he texted that he had left and disco'd the charger. I went back the next day and checked both batteries while hooked up in the vehicle and they were reading 12.45.. Took the batteries out of the vehicle system and the right battery was now at 12.55 and left battery at 11.50 and dropping. Hydrometer test showed one bad cell. It is a NAPA house battery, about 5 years old.

I'll replace the battery with a standard auto battery as I have a trip coming up in a couple weeks with the 80, unless I can find a dual purpose 27F. I've got most of the setup to isolate the batteries (Blue Sea ML-ACR) and have contemplated adjusting the wiring so I have two standard 27 series RV batteries in place, whenever I get around to the install. Not to open this debate as is discussed on other threads; I've not decided if I want one battery completely free of load when the truck is not running, or split the load with all vehicle on one side, and house/extra loads on the other. The system will have at a minimum a 100 watt solar panel as well.

I've got two of the micostart batteries. This summer the diesel Dodge was deader then a door nail due to user error. Before the jump...nothing was working, not even a click on the starter relay. So I put one of the Anti Grav units on the left battery (it had been sitting for well over 6 months but showed full charge) and tried to start. Cranked a few revolutions then click click click. Waited a minute and tried it again...same result. It now showed three bars. Left it hooked up and put one of these on the other battery: Mini Multi-Function Jump Starter The AL-JP16 had been plugged in for months. With both hooked up it cranked a few times and started.

I wonder if the micro battery that was plugged in till used would have done it on its own. (I did not volt meter the truck batteries before hooking things up, but after running for 4-5 minutes then sitting for a minute or two they read 11.3 and 11.4 so they were down quite a bit)

hth's
gb

 

[LandCruiserPhil]

I've not been running my 80 much lately and have had it at the shop with a Deltran Battery Tender Plus hooked up all the time. Batteries hooked up full time in parallel. Every time I pop by the shop I check the batteries. Through the summer I noticed it was in charge mode more then I thought it should be (no loads). A week ago when I went to install an awning it was in storage mode. Started and moved the vehicle and when done I put it back, with the charger hooked up. Stopped by the other day and noticed the charger was smok'n hot and the batteries were at 12.50(ish). I asked my shop mate to keep an eye on it till he left and disco it if still the same. Couple hours later he texted that he had left and disco'd the charger. I went back the next day and checked both batteries while hooked up in the vehicle and they were reading 12.45.. Took the batteries out of the vehicle system and the right battery was now at 12.55 and left battery at 11.50 and dropping. Hydrometer test showed one bad cell. It is a NAPA house battery, about 5 years old.

I'll replace the battery with a standard auto battery as I have a trip coming up in a couple weeks with the 80, unless I can find a dual purpose 27F. I've got most of the setup to isolate the batteries (Blue Sea ML-ACR) and have contemplated adjusting the wiring so I have two standard 27 series RV batteries in place, whenever I get around to the install. Not to open this debate as is discussed on other threads; I've not decided if I want one battery completely free of load when the truck is not running, or split the load with all vehicle on one side, and house/extra loads on the other. The system will have at a minimum a 100 watt solar panel as well.

I've got two of the micostart batteries. This summer the diesel Dodge was deader then a door nail due to user error. Before the jump...nothing was working, not even a click on the starter relay. So I put one of the Anti Grav units on the left battery (it had been sitting for well over 6 months but showed full charge) and tried to start. Cranked a few revolutions then click click click. Waited a minute and tried it again...same result. It now showed three bars. Left it hooked up and put one of these on the other battery: Mini Multi-Function Jump Starter The AL-JP16 had been plugged in for months. With both hooked up it cranked a few times and started.

I wonder if the micro battery that was plugged in till used would have done it on its own. (I did not volt meter the truck batteries before hooking things up, but after running for 4-5 minutes then sitting for a minute or two they read 11.3 and 11.4 so they were down quite a bit)

hth's
gb

Good info▲

As for the Antigravity jump starter. Some claim it would not jump start. I sight the operator in most cases. When a battery is dead (no click) I found you must disconnect the battery from the vehicle. Hook your jump start clips to the battery cable (only one side needs to be disconnected from battery) and it will start. Once started hook your battery cable back up while it is running. When you hook an Antigravity jump box to a dead battery it will suck too much power trying to bring the dead back up and does not have enough to do both and start the vehicle. If you go to start your vehicle and get a slow crank ~10.5-11 volts disconnecting the battery cable normally is not needed. Just jump and go.

 

[cruiserpilot]

Greg in the second paragraph you say 'unless I can find a dual purpose 27F'. What do you mean? I know I have dual
27 series on my 60. One is a 27 and I think one is a 27F meaning the terminals are switched for usage, one
battery LH and one battery RH. Is that what you mean? I've looked up specs and I find that when I find a 27 and
a 27F, one of them always has more CCA and a higher reserve. Why is that?

I also find it interesting that people leave the batteries hooked up when the vehicle sits.
Mine regularly sits for 2+ months. I remove both leads from both batteries. I've never come
home to a dead or low power battery. I hook up and start up.

 

[Greg_B]

Greg in the second paragraph you say 'unless I can find a dual purpose 27F'. What do you mean? I know I have dual
27 series on my 60. One is a 27 and I think one is a 27F meaning the terminals are switched for usage, one
battery LH and one battery RH. Is that what you mean? I've looked up specs and I find that when I find a 27 and
a 27F, one of them always has more CCA and a higher reserve. Why is that?

I also find it interesting that people leave the batteries hooked up when the vehicle sits.
Mine regularly sits for 2+ months. I remove both leads from both batteries. I've never come
home to a dead or low power battery. I hook up and start up.

I mean RV/Marine dual purpose (hybrid compromise of starting and deep cycle). This is not endorsement of Trojan batteries...just for reading reference: http://www.trojanbattery.com/pdf/TrailerBoats_batteryguide_201105.pdf

I too in the past have unhooked batteries from vehicles if not using for a long while. And if I did not have easy access to power during storage whould unhook them as well. With the smart chargers nowadays I figure if I can leave it hooked up and have the batteries optimized (bulk charge and then maintenance charging while in storage) they should last longer.

As for the Antigravity jump starter. Some claim it would not jump start. I sight the operator in most cases. When a battery is dead (no click) I found you must disconnect the battery from the vehicle. Hook your jump start clips to the battery cable (only one side needs to be disconnected from battery) and it will start. Once started hook your battery cable back up while it is running. When you hook an Antigravity jump box to a dead battery it will suck too much power trying to bring the dead back up and does not have enough to do both and start the vehicle. If you go to start your vehicle and get a slow crank ~10.5-11 volts disconnecting the battery cable normally is not needed. Just jump and go.

Thanks for the info.

gb

 

[atomicshawn]

I've wanted to pick up a set of brushes to throw in the bag, but I keep putting it off. I'm going to get it done this week...

$19 worth of insurance. A little extra peace of mind.

 

[Fishinfortuna]

Dual battery setup is the next mod on my list. Thanks for sharing your story.