Second Battery Question

D

dharte

Senior Member
Joined
Dec 8, 2015
Messages
161
Hi folks,
In my recent thread about adding a fridge, I mentioned I would be adding a second battery to my 2015 Hawk set-up which has the 165W solar panel and one battery. I have two questions:

1. Is there any harm adding a brand new battery to the 2 year old battery I am using (Exide AGM)?
The two year old battery has been charged it's entire life with the solar panel and has never been run
low.

2. Is the camper pre-wired for two batteries, or will I need to add cables from the old battery in parallel to the new battery. The battery in use has two connectors on each post, but I think one is from the solar controller and the other set is the main camper power cables. Not sure though since I don't have a schematic to look at. One of the positive cables has a built in fuse holder on it but not the other wire.

Thanks,
David
 
My 2¢ worth. It’s not best practice, but it won’t be catastrophic. The older battery might be weaker, and draw down the other. I suspect you’ll have to change them out at different intervals. If you have another use for the existing battery, you might use it there, then install two matched batteries in your camper.
 
Wandering Sagebrush said:
My 2¢ worth. It’s not best practice, but it won’t be catastrophic. The older battery might be weaker, and draw down the other. I suspect you’ll have to change them out at different intervals. If you have another use for the existing battery, you might use it there, then install two matched batteries in your camper.
Click to expand...
I would agree. If possible, use the original battery in another application. Otherwise, just go ahead and wire in parallel
 
I doubt that it is wired for two batteries, but assuming that there is the physical room for the second battery it shouldn't make much difference.

Another best practice, but not an absolute, is when wiring two batteries in parallel to make the + connection on one battery and the - connection on the other. If the existing wires allow it, then do it. If they do not, then don't bother and don't fret about it either.
 
Yikes, the original battery (Exide Edge) is $315 on Amazon. Anyone know a more affordable brand/place to buy a deep cycle rv battery? No luck on the car parts store websites or Sears.. I will not use Optima batteries due to very poor lifespan when I used them in my truck.
 
dharte said:
Hi folks,
In my recent thread about adding a fridge, I mentioned I would be adding a second battery to my 2015 Hawk set-up which has the 165W solar panel and one battery. I have two questions:

1. Is there any harm adding a brand new battery to the 2 year old battery I am using (Exide AGM)?
The two year old battery has been charged it's entire life with the solar panel and has never been run
low.

2. Is the camper pre-wired for two batteries, or will I need to add cables from the old battery in parallel to the new battery. The battery in use has two connectors on each post, but I think one is from the solar controller and the other set is the main camper power cables. Not sure though since I don't have a schematic to look at. One of the positive cables has a built in fuse holder on it but not the other wire.

Thanks,
David
Click to expand...
+1 to what the other's said, and yes, you will need to add wires.
 
I also agree with what Wandering Sagebrush (and others) said above. When you parallel your batteries, consider a minimum of 6 AWG wire for the parallel connections. If you have enough existing wire in the battery box (and you should), I would follow what ntsqd recommended about using the + on one battery for the camper +, and the neg on the other battery for the camper neg. This equalizes the load on the batteries.

When I went from one to two batteries I bought Exide AGMs from Bi-Mart for a very good price (don't remember what it was, but WAY less than Amazon). I have also seen them either at Home Depot or Lowes (I think it was Home Depot).
 
Suggest searching the type and group size batteries that you want on the whole net. By doing that I found a place where the shipping was included in the price, and they were still way better priced than anything local.
 
Well after a lot of research, I am really thinking about getting 2 6v batteries and connecting in series, I found some that will fit for about $200 each. They have the same footprint as the group 24, but are taller, and my battery cabinet has lots of space above the batteries. This shouldn't pose any issues for the solar charger should it?
 
I applaud your choice of two 6 volt batteries.
We have them in our Hallmark and they have been very reliable so far.
 
dharte said:
Well after a lot of research, I am really thinking about getting 2 6v batteries and connecting in series, I found some that will fit for about $200 each. They have the same footprint as the group 24, but are taller, and my battery cabinet has lots of space above the batteries. This shouldn't pose any issues for the solar charger should it?
Click to expand...
Existing charger should have no problems. Your batteries will appreciate the best, fully adjustable charger you can get. Victron or Trimetric are good choices. I have dual 6v batteries and they are awesome. Which batteries?
 
Vic Harder said:
Existing charger should have no problems. Your batteries will appreciate the best, fully adjustable charger you can get. Victron or Trimetric are good choices. I have dual 6v batteries and they are awesome. Which batteries?
Click to expand...
Amstron GC2. I ordered them on Amazon.
 
Vic Harder said:
Good stuff, as it comes with spec sheets! https://www.amstron.com/content/AP-GC2_Specification_Sheet.pdf
Does your solar charger have adjustable settings to accomodate the specific voltages and currents this spec sheet lists?
Click to expand...
I don't know if it's adjustable-it's the one FWC installed with the panel. I do know it currently charges at 13.4v, and that's close to what the specs list (13.2) on the new batteries (when hooked in series of course). Vic, is yours adjustable?
 
Yes it is. 0.2v doesn't sound like a lot, and it might not make a difference depending on how long you want those batteries to last. I have roughly the same setup, 2 6v 220 AH batteries. Like yours, the cost a fortune, so I think spending another couple hundred bucks on a good charging system and monitors for it might be worth doing.

Like a few other folks here, I am using Victron gear. Love it.

For reference, you have 165W of solar, and are now adding a fridge (2 way?). With my 265W on the roof and my 130L two way fridge, I have NEVER discharged my batteries below 80% (OK, I have, but just once, during a test) in 42 days of camping.
 
Clemson,

The answer is mostly due to weight of the individual batteries.

In a nutshell a 12 volt 220 Ah true deep cycle battery weighs about 120 pounds. Two 6 V 220 Ah true deep cycle batteries can give you the same power but the batteries only weigh 66 pounds apiece. Clearly the 6 V batteries are easier to move into a camper.

Similarly if you only wanted 100 Ah, each 6 V battery is about half the weight of the 12 V. In the end the total Ah and weight is pretty much the same for one 12 V or two 6 V.

Now this is for lead acid batteries - i.e. flooded lead acid (FLA), Absorbed Gas Matt (AGM) and Gel.

If you spend a lot more money you can get a Lithium Iron Phosphate (LiFePO4) battery which weighs about half as much as a lead acid battery with the same Ah and at the same time get a lot more and deeper discharge cycles on the battery than you can on a lead acid battery before you degrade the battery. But LiFePO4 are still about 3x or more the cost of a high quality deep cycle lead acid battery.

I hope that helps,

Craig
 
With the 2 6-volt batteries I'll have 210 amp-hours, as opposed to 150 amp-hours with 2 12v group 24 batteries. The 6-volts are about 20 pounds heavier and taller but have almost the same footprint so they will fit in the cabinet in my front dinette Hawk. Since I needed to buy two batteries anyways, I figured this is the time to switch. I will be installing a 2-way fridge this week and don't want to worry about running out of electrical juice (or cold beer)!
 
dharte, et al,

You may already know the following but just in case and for folks reading who don't: group 24 is a case size and group 24 batteries are frequently starting batteries not true deep cycle although they can be deep cycle (be sure to check and verify).

There are significant differences among starting batteries, hybrid starting deep cycle batteries and true deep cycle batteries. It is important to know the difference in terms of depth of discharging and lifetime.

http://www.wanderthewest.com/forum/topic/15574-ultimate-battery-thread/
 
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