Adding a deep cell?

Stick it in your battery box and use an Isolator.

 

There is no easy way. You have to start adding in relays to connect the battery for charging, but disconnect when cranking and so on. It can be done, but more headaches than what it is worth.

 

All it takes is an isolator(asically a big ### relay specifically made for this very reason), invest in a good one, follow the instructions, and thats it. If you are uncomfortable with wiring for this type of setup, pay to have it done at a reputable shop. No need to put your life or the one of those who park near you in danger.

 

This is one of those things that look good on paper or in theory but just seems to suck in real life. The wiring and parts installed need to be tip top quality. Starts to get expensive to point where it isn't worth the cost. Then guys start to cheap out and electrical problems start and you're chasing gremlins all the time. I'm sure for some they are a great idea and successful, but over my career I have taken out way more than installed.

 

Well I can also tell from experience that it will get expensive. Every time you drain a battery no matter how good the battery, you stress it out and weaken it. Yes I know, pulling down by the bon fire in your pickup and turning on the radio and after killing a 5th of old no. 7, you realize you forgot to start it up from time to time to charge it! So far 3 years, 2 batteries @$230 a pop. You get my point.

 

If a proper isolation system only looked good on paper it would not be used in campers, RVs and trucks all over the country. Hundreds of thousands of them. The biggest issue is people being cheap and not using the proper parts. It will cost more but if you buy from a good company you will get a product that performs well and provides no issues. Plenty of the drivers I know run at least one spare battery. At least those who didnt spring for an Apu. When working with these things even cheaping out on the size of wires used will cause problems. Do it right once and you wont have to rip the system out. If you do go this route and consider putting your battery under the bunk, make sure you vent it.

 

I have the "Nite" A/C and heat system on my truck that's runs of 4 deep cycle batteries. All you need is a good isolator switch that will cost you in the 200-250 $ range. Nothing is complicated here, when using in cab power it will drain only your deep cycle batteries, and when your truck is running, once your main batteries reach 13.5 volts isolator switch will open circuit and charge your aux batteries. If current drops below 12.7 in main batteries circuit will close to keep charge in main batteries. All this is done by a good quality isolator switch

 

the easy way is tu use D+ output of alternator to connect battery to charge only when engine runs.

 

I used to use 2 deep-cycle batteries in my truck along with the starter batteries. They are good for running a fan in the window, some low-current lighting, laptops, etc. I made up a harness with a 'Ford Starter' relay (very cheap), to engauge them when the truck key was on. They worked great for what they did, but now I use glass-matt AGM's instead. Those things are like the 'Hercules' of any other battery I ever tried. They can be purchased much less from a marine dealer than from a truck supplier. They are used heavily on sail-boats these days.

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some info on batteries...
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Vibration and motion may not be so good for your connectors but it
actually helps batteries. Lead-acid batteries actually perform better when the acid
gets regularly 'stirred up' by the motion of a vehicle. Did you know there are 3
basic types of batteries for trucks? There are starting batteries, deep-cycle
batteries, and hybrid batteries. Most trucks you see have starting batteries. These
type of batteries are designed to provide a lot of power all at once in quick, short
bursts. Most of the time they are rated more for their 'Cold Cranking Amps', rather
than for their 'Amp Hours'.
All lead-acid batteries loose the amount of power available as they get
colder, so starting batteries with really high 'Cold Cranking Amps' will help get
your truck started in below freezing temperatures. The downside of these batteries
is that they are not designed to provide constant power. The more powerful the
cold cranking amps that a battery has, the thinner the lead plates are inside the
battery. They make the plates thin so that more of them can be placed inside. The
more plates, the more cold cranking amps. Because they are so thin, it is easy for
them to overheat internally when there is a slow, constant drain on them. This
means that when your truck is turned off and you are using power from them to
run an inverter or anything else that needs a significant amount of constant power,
you are likely shortening the useful life of those batteries. It should also be noted
that most starting batteries will only tolerate being completely discharged a few
times before being irreversibly damaged.
Deep-cycle batteries are designed to provide power on a more constant
basis. The lead plates inside these batteries are thick, keeping them from
overheating, but because of this, they have a lot less cold cranking amps. This
means they will make starting your truck a bit harder, especially in colder
weather. You can certainly use deep-cycle batteries in your truck if you need more
constant power, but you might need to do a couple of things to ensure you do nothave problems. It is possible you may need to add an extra battery to overcome
the lower cranking amps, and/or you might also need to replace your starter with
an after market 'Geared Starter'. Geared starters require a lot less cold cranking
amps to get your truck started. Denso makes some pretty good after-market gear
reduction starters for class-8 trucks, so if your starter ever does go out, it wouldn't
be a bad idea to get one of these vs another OEM.
Hybrid batteries come in a few different flavors. They are an attempt to get
the best of both high 'Cold Cranking amps' and still provide a decent amount of
continuous power without overheating. Sometimes these type of batteries are
referred to as Gel-cell, Nickel-Cadmium, or Glass-Matt (AGM) batteries.
Gel-cells are pretty good batteries for extreme environments and off-road use, as
the liquid inside is fixed in place. One of the problems with gel-cells though, is
they can be damaged very easily from constant charge/discharge, or from
overcharging. If your alternator produces a slightly high voltage, then it is likely
that gel-cell batteries will have a short lifespan in your truck. Nickel-Cadmium
batteries are more like Deep cycle batteries except they offer more
charge/discharge cycles before they go bad. The downside of them is that they
consume a lot of excess energy while charging, costing you fuel. Glass-Matt,
otherwise known as AGM batteries, are usually much more expensive. With their
higher price, comes some pretty good benefits though. They are tough, like gel-
cells, but they charge more like starting batteries, as well as providing the ability
of constant power. They are actually about 25% more energy efficient than any
other type of truck battery, actually assisting you in saving fuel as well. These
type of batteries are definitely the way to go if you plan on installing any type of
sizable inverter because they will pay for themselves long term both in lifespan
and energy savings.
No matter what type of batteries your truck has, to be cost effective long
term, you need to always ensure that the batteries are not only of the same type,
and capacity, but also close to the same age. Keeping your batteries as a 'Matched
Set' as much as possible will increase their lifespan greatly. As a comparison to
this analogy, think about your truck engine for a moment. What do you think
would happen if each cylinder of your truck engine was a different size and/or
type. Your engine would not only run very rough, but the cylinders doing the most
work will always cause you the biggest problems. Truck batteries need to be the
same capacity, type and roughly the same age to ensure they perform together as a
group. Buying used batteries, and/or mis-matching them will only result in more
battery problems long term, costing you unnecessarily.

quoted from...
http://mastergeeks.opendrive.com/fi...ime Class-8 Lease-Purchase Owner-Op Guide.pdf