Adding a 2nd battery

If I am to park for more than 1 night in one place without hookup or a lot of sun then I'm going to need a 2nd battery.

Unfortunately there is no space to fit it. So the only option I can see is to do this:

Take a battery cable, connected in parallel with the existing battery, out to one of those high amperage connectors (the type people use for connecting demountable winches etc.) that I would mount under the cabover step.

Fit another 12v battery into a portable battery box with a similar battery cable to a mating connector.

I could then leave this 2nd battery plugged in full time, in parallel with the main battery, but move it around inside the camper depending upon where it is least inconvenient at the time, e.g. under the dinette, on top of the couch, etc. and when access is needed remove it altogether.

My reasons and restrictions are as follows:

1) I don't have space for the 2nd battery outside the camper.
2) I don't want a battery that I only plug in occasionally - I can imagine that going flat sitting in the garage while the other one stays charged up from the permanently connected solar.
3) But I want to be able to disconnect it while working in the camper.
4) I am sticking to old fashioned 12v lead acid batteries for the moment - I want something easy to charge from the alternator / solar / battery charger.
5) Over here a generator is not an option - campgrounds don't allow them.

However, some questions, not being an expert on lead acid batteries:

1) I'll use good thick starter-motor cable between the batteries, but it will still be around 5 foot in total (with a connector in between). This will lead to a bit of voltage drop. Is this likely to cause me a real problem? To reiterate the charging voltage will be applied directly to the terminals of the original battery, but then cables will take that from there along to the 2nd battery. I am aware that if the 2nd battery was permanently wired I wouldn't do it as I would want to ensure the voltage was consistent across the batteries.
2) My current camper battery is over a year old. Do I need to buy two identical batteries when I do this rather than just adding a 2nd brand new battery to an older existing one?

Thanks in advance,

Steve.

Truck Campers

full_mosey
Explorer
Sep 02, 2013
sleepy wrote:
You can't get a full charge at 14.1 VDC... you must have 14.4 VDC

...

This web page Battery User Guide will lead you to the PDF file. The first chart says 13.8 - 15 Volts. So YES, you can charge at 14.1.

HTH;
John
sleepy
Explorer
Sep 02, 2013
You can't get a full charge at 14.1 VDC... you must have 14.4 VDC

The literature that comes with my optima batteries and other AGMs tell you that you can charge at 14.8 VDC... with a good solar system you won't have any problem supplying the 14.8 VDC

If you notice I have battery warmers.... the optimum temperature for all batteries is 77ºF or 25ºC

(read the literature that comeswith all batteries... this is their advertized capacity @ test temperature )

colder you lose capacity
hotter you increase resistance
full_mosey
Explorer
Sep 02, 2013
sabconsulting wrote:
AGM does sound like a good idea. My batteries get charged from the cable running from the truck + solar. Are there considerations regarding charging voltage for this set-up?

Steve.

The only charging issue is you don't stir the liquid in an AGM. This is sometimes called equalization. The process uses higher Volts to force bubbling. Simply un-select any thing like that on your charging sources.

Usually AGM's manuals want a temp compensating charger to manage Volts. Higher when cold and lower when hot. If your solar controller doesn't do that, set the solar controller for 14.1V when it is hot, above 90F, and 14.4V otherwise. I have 2 x Optima 55AH and an 79AH Deka. The details are in my profile.

When installing AGMs, it is not necessary to place them upright, they can be placed on an end or side. Here is a Johnson Controls pdf that gives sizes and AH specs.

HTH;
John
sleepy
Explorer
Sep 01, 2013
sabconsulting wrote:
AGM does sound like a good idea. My batteries get charged from the cable running from the truck + solar. Are there considerations regarding charging voltage for this set-up?

Steve.

You need to charge lead acid batteries at 14.4 VDC

My AGM batteries can be charged at 14.8 VDC and thats what I do...

Mine are 10 year old Optima group 31's... and they still take 100% charge according to my Trimetric. I NEVER let them discharge below 50%.... secret learned from Toyota Prius.

Chet
sabconsulting
Explorer
Sep 01, 2013
AGM does sound like a good idea. My batteries get charged from the cable running from the truck + solar. Are there considerations regarding charging voltage for this set-up?

Steve.
sleepy
Explorer
Sep 01, 2013
In a dual battery system you would normally have your system wiring connect to the positive post on one battery and the negitive post on the other battery to get the electons to flow through each battery as evenly as possible during charging and discharging.
sleepy
Explorer
Sep 01, 2013
I should have explained the reason that I used 2 different type and color of th connectors in the link above:

It was so that there is absolutely no way to "quick connect" anything wrong.

I used a couple of different colored pens (to match the connectors) to draw the potential wiring diagram before ever buying the parts.

Then inserted the connectors into the schematic (still on paper)

Steve with your set up you should be able to:

1) have a single battery system

2) have a dual battery system

just by unplugging the wireing in the single battery system and plugging in the second battery to have the dual battery system.

Reverse to return to the single battery system

Note: I also used quick connects to connect the primary battery to the charger....

and the solar system

and I used only one side of a connect (they are polarized) for some particular reason to make my system work.

My Trimetric had to be included in the schematic too.

Bottom line... make it work on paper.
sleepy
Explorer
Sep 01, 2013
Steve

I think that it is extemely importantant that the parallel wiring between the two batteries be as equally matched as to length (and resistance) as possible.

i.e., the neg to neg and the pos to pos wires need to be exactally the same.

And... the Anderson quick connects work well... they match the wire gauge.

I agree that audio shops have the best wire, fuses, and connects

I added a link where you can see the ones that I recommend

I think that you should consider a pair of AGM's... hydrogen gas from batteries inside your camper is too risky. Sally is much too precious to risk.

sleepy
tplife
Explorer
Aug 31, 2013
The advice above, while in many respects is good, should be ignored regarding AGM batterie...Unless you sell old-school 20th century lead acids jobs and live off the commissions...:B
tplife
Explorer
Aug 31, 2013
wintersun wrote:
Most important with a second battery is having both of the same type whether it is two AGM or two flooded lead acid type. Problem often is that the place where the second battery needs to go is not one that can be vented or where it is not easy to get to the battery to add water so the solution becomes to get two AGM batteries.

With the Torklift solution you could use a flooded lead acid battery which is cheaper and likely to last longer than an AGM type. If the isolator for the truck battery is under the hood then you can link the battery under the frame in parallel to the battery in the camper and both will be charged by the truck's alternator or shore power.

People tend to use much too heavy a gauge wire than is necessary and this adds to more cost, more difficulty in finding and attaching terminal connectors, and a lot more difficulty in feeding the wires from point A to point B. What is often not understood is that the current carrying capacity of the wire depends upon the area of its cross section and not the diameter of the cable. There are 12 foot jumper cables made using 8ga wire that work perfectly well.

For a 20 foot run for DC the use of 2ga wire results in a current loss of 0.53%. Using 8ga wire the drop is 2.15%. Seems like a lot at 4 times the drop but if you think about it in terms of charging time, the difference between 1 hour and 1 hour (60 minutes) or 61 minutes and twenty seconds with smaller wire is trivial. All you need is wire thick enough to handle the Watts being drawn so it does not overheat.

Big difference in ease in finding battery connectors for 4ga wire which is standard and for 2ga wire which is not in the car and pickup world. Even more choices with 8ga wire. Great source for wire and connectors is delcity.com or if you want marine grade wire, Jamestown Distributors.
This is a post to ignore - Your hard-e4arned money when buying an AGM battery means typically 2X the life due to major differnects is constructon. I am on my 3rd AGM battery and I'm not ever going back to 20-th century old-school lead-acid stuff...Do a bit of researech and join us...

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