The Transnistria parliament building with a statue of Lenin out front. In the city of Tiraspol, Transnistria. Photo taken December 9, 2016.
Where are Kevin and Ruth right now? Tiraspol, Transnistria...the country that doesn't exist.

Where are they going next? Northern Moldova. Arrive December 11th.

Saturday, August 6, 2016

We didn't understand 12 volt batteries!...Part 2

In yesterday's blog post we talked about your RV's battery and 12 volt electrical system. We're trying to stick to the basics, and we're trying to explain everything in terms that the average person will understand.

Today, we'll get into the most popular different types of batteries.

When your RV is new, it likely comes with one or possibly two house batteries. (Motorhomes will also have a separate battery for starting the engine.)

It is also likely that the battery in your new RV is not the best quality. It's probably a 12 volt "marine" deep cycle battery, which is not a true deep cycle battery, and not a very good battery for long term life. You can buy these marine deep cycle batteries for under $100 at Walmart. If you abuse these batteries by constantly drawing them down below 12.1 volts (as explained in yesterday's post), they won't even last a year.

The next step up in quality and durability is to buy two wet cell deep cycle 6 volt batteries. If you wire them together in a "series" configuration, you get a 12 volt output. This is the most popular configuration for RV'ers who want to upgrade the quality of their battery system.

On the outside, a 12 volt battery and a 6 volt battery look very similar...

12 volt marine battery

6 volt true deep cycle battery.

They look pretty much the same, right? Slightly different in size, but they look essentially the same.

But on the inside, they are quite different. Here's why...

Each battery is made up of lead cells on the inside. Each cell produces 2.12 volts when fully charged. Remember from yesterday that we told you that a fully charged 12 volt battery reads 12.7 volts? Well if we do the math, we figure that there must be six cells in a standard 12 volt battery. (6 x 2.12 = 12.72). 

And that means that in a 6 volt battery, there must be 3 cells.

Because the 6 volt battery and the 12 volt battery are essentially the same physical size, the lead plates that make up the cells can be much thicker in the 6 volt battery than they are in the 12 volt battery because there are only 3 cells in the six volt battery, whereas there are 6 cells in the 12 volt battery..

And because it is the deterioration of the lead plates that causes most batteries to fail...the 6 volt batteries will outlast the 12 volt batteries given the same usage.

There is a wide price variance in these batteries, but if you shop around you should be able to buy these batteries for under $140 each.

The Trojan T-105 is the battery that we use. We use our battery system almost exclusively for all of our power since we are rarely plugged in at a campground. We have four of these batteries in our system, and they are now six years old and still operating perfectly. Since they say that the average lifespan for these batteries is 3 to 5 years, we're doing pretty good!

You can go a next step up though. You can buy Absorbed Glass Mat (AGM) batteries.

These batteries are quite a bit more expensive, typically costing between $200 and $300 each. I think that it's hard to justify the extra cost, since the benefits are only useful in certain situations. 

The main benefit of AGM batteries is that they are sealed. That means they can be installed upside down or sideways if you wish. They are also maintenance free, not requiring the regular inspection and watering that the wet cell deep cycle batteries require. They also charge slightly faster. They are certainly a top quality option, yet it is hard to justify the extra cost.

That's enough for today. Tomorrow, we'll get into charging systems.

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22 comments:

  1. We have the same trojan batteries and they do an awesome job, ours about the same age as yours, and still perform like new.
    Another great posting.

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    1. Glad that you like the Trojans as well. We feel they are definitely worth the extra money especially if you do a lot of boondocking and have a solar set up.

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  2. I have always intended to buy the Trojan batteries but have been tempted away by the lower price of the Sam's Club and Costco brands that are available for much less. The last pair I bought in April in Washington State for $90 CA ($70 US) each. However, I get less service time from them than you and George get from your Trojans. My last pair lasted four years. Maybe next time I will try the Trojans.

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    1. Glad that both George and Kevin have got you thinking about the Trojan batteries. I know we haven't regretting buying them.

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  3. A benefit of good AGM batts is being able to repeatedly take them down to 11.8 volts. The other is that I no longer have to put up with sulfuric acid vapors coming out of the battery when charging and causing corrosion.

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    1. Plus, I now have three pair of shorts with battery acid holes burned in them from servicing batteries.

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    2. I guess you could say that you, Barney are convincing us on buying the AGM batteries much like we are trying to convince others of buying the Trojans. ;-)

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  4. Big box store batteries are also notorious for exaggerated amp-hour ratings---they often hit the critical 12.1V much sooner in the evening than the Trojans.

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    1. Another reason to go with the Trojans!

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  5. Like air conditioning compressors, there are only three major battery manufacturers in the world and Johnson Controls is the largest. The manufacture for CostCo, Sam's and many other brand names. I bought Kirkland (Johnson Controls) here in Mexico for $95 each. They are on their sixth year. BTW, there is a corporate office for Johnson Controls right here in Monterrey, Mexico along with several manufacturing plants.

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    1. I have Sam's Battery's in my golf cart and still going strong after seven years !
      Trojan way over rated !

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    2. You guys are starting to make me feel better for being a little cheap.

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    3. The problem is that it's so difficult to compare apples to apples. From the research I've done, I'm fairly confident that the Trojans are the best and that you know what you're getting. However I'm not sure that they're worth 25% more in price.

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    4. My just done research tells me that the Trojans outweigh the Costco's by ten pounds (67 lb vs 57 lb) That means there is probably more lead in the Trojans although the case might be slightly heavier as well. More lead makes me think more capacity but it does all come back to your observation of are they worth 25% more $.

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  6. Just buying 2-6v deep cycle batteries because people said better than 12v
    now I understand thanks why
    thanks for the acticle

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    1. So glad that we have helped you to understand the differences with the batteries.

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  7. One specification that is often overlooked is the weight of the battery. The heavier the battery the more lead in the cells and as Ken said the more lead the battery has the longer the charge will last. I bought a golf cart last year that had Costco marine deep cycles in it brand new....didnt last 6 mths. Going with new Trojans this year.

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    1. Very good point! We are certainly very happy with the Trojans that we bought so many years ago, and I am sure you will be much happier with them too.

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  8. Went to AGM batteries last year. Will never go back to the open wet cell. The AGM charges faster and last longer with less/no maintenance. Yes they were more expensive but worth every dollar IMHO.

    rocmoc n AZ/Fld/Baja

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    1. Who knows, that may be the way we go as well whenever the batteries we have finally give up the ghost. That's for your input.

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  9. Love the diagram of the 12v system. Thank you! I too am ignorant of the system in general and we are converting a large bus into a live aboard. If anyone would like to post a basic plumbing diagram, that would sure be useful as well. Thanks again for the great posts. Much appreciated!

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    1. Sounds like you have a big project on your hands! Hope that our posts on the battery system and solar will be of help. Sorry we can't help you out on the plumbing side of things. There are groups on facebook that can help with RV plumbing and makeovers/conversions and I am sure if you google "diagram of plumbing in an RV" you might find something that can assist you. Good luck and have fun making your bus a home.

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