Battery groups?

[morgynm]

What is the difference between a group 24, group 27, and group 31 battery? Is there a recommended size for our little trailers?

Athough I don't really need one, I think I might replace my current one with an AGM battery because it's kept under my dinette seat.

[Timber Wolf]

The 24 is a standard size car battery, the 27 is a little bigger and what I use in my pickup. The 31 is a little larger still than the 27 but still managable and what I use in my farm tractor. If I was only going to have one I would go with the 31 as it is not that much bigger or more expensive than a 27 and will usually fit similiar size boxes. But seriously, a single battery is so over. All the cool kids are running dual 6V batteries these days.

[blodn1]

All the cool kids are running dual 6V batteries these days.

I just have a problem with this. In the rare event that one battery goes down, the entire electrical system is out. Fairly inconvenient, even if another 6V is readily available.

[Timber Wolf]

Originally Posted by blodn1

I just have a problem with this. In the rare event that one battery goes down, the entire electrical system is out. Fairly inconvenient, even if another 6V is readily available.

Aren't you in the same boat if your single 12V battery goes down?

[blodn1]

Tim - you have a good point :-)

On my (future) Oliver, I'll have three 12V batteries, instead of four 6V, so only 1/3 of the system will go down with failure of one, instead of 1/2 the system.

[Frederick L. Simson]

List of Common Battery Case Sizes | BCI Group Numbers

Originally Posted by LINK

You may have heard common terms like a "group 24 battery" or "type 27 marine battery". These numbers are referring to the BCI Group Number of the battery. These numbers define the physical dimensions of the battery case. This is important as some applications call for specific case sizes. The BCI does not determine the Amp Hours (AH) rating for the batteries, however, but there is a correlation between case size and AH rating. For deep cycle batteries, the larger the case size the more capacity the battery will usually have.

[Carol H]

Originally Posted by morgynm

What is the difference between a group 24, group 27, and group 31 battery? Is there a recommended size for our little trailers?

The difference is the amp hours of each as well as a size and weight. Although it may not be what the new cool kids on the block are going with a great many of us with small 17' and under trailers are getting by very comfortable for hundreds of nights of camping a year with a simple deep cell group 27.

[The Minimalist]

Actual term is BCI Group Size and specifies the length, width and height of the battery. Below are the standard BCI Group Sizes used in TTs. The last is the venerable 6v golf cart batteries, used in pairs.

You may find some minor differences among manufacturers for a given group size. I believe BCI have a min/max on the dimensions, but they should be relatively close. If it looks like a close fit, measure the box and battery before purchasing.

Fred: It looks like they boggled the length and height for the GC2 in the link you gave.

Within a given size envelope there are a number of factors, i.e. number of plates, plate thickness, plate composition, etc. that determine the actual electrical characteristics of the battery.

In a TT what you want to do is get the largest group size battery you can fit in the box, and your budget, with the most amp hours of capacity you can expect. Look for deep cycle batteries(fewer but thicker plates) with specified 20hr amp hour ratings. There are other ways to calculate amp hours, but usually if it specifies 20 hrs,the batteries have actually been tested at this rate and it is the standard for deep cycle batteries. Some battery manufacturers will give you apples when you specified oranges.

[morgynm]

I'm lost! Got that the numbers just indicate the size but you lost me on the amp hours.

Here's the battery I'm looking at:
http://m.canadiantire.ca/en/pdp/grou...-0102498p.html

It says 75 amp hours. We only camp on the weekends at this point in our lives so this will do for now?

And what is the difference between having one 12v vs two 6v? I've seen the 6v mentioned in other threads so I've been very curious!




Morgyn
1981 13' Boler
Nova Scotia

[The Minimalist]

Sorry for the confusion. First, folks use the dual 6 volt batteries connected in series to give them more amp hours at 12 volts. The typical GC2 golf cart batteries have 185 to 220 amp hours or so, and are great if your power demands require it.

As far as how the 75 amp hour battery serve your needs, we need to know what kind of loads you will put on the battery and the approximate hours of usage for each. I've seen from earlier posts that you are using LEDs. Good move. Those typically draw .2 amps or less.

I assume you are boondocking, as the battery is not an issue if you have shore power. So, how will you be charging the battery? Solar?

So, lets get a list of your loads and usage times and we'll work it out from there.

I'll say this. I'm operating with a Group 24 marine deep cycle battery with 86 amp hours, charged with 85 watts of solar panels. Spent 10 days in the Smoky Mountains with no hookups and everything was fine.

[morgynm]

Thanks for the help!

Since I'm having a hard time realizing that my Boler isn't just a large hard sided tent, I don't think our electrical needs are much.

We have one double light fixture, two singles, and the porch light. All converted to LEDs. My husband and I both have iPhones that we charge every night. And the fan I just ordered. Its kind of vague but it says 12 watts.

I think that's it for now. Oh, and the fan in the power centre.

Morgyn


Morgyn
1981 13' Boler
Nova Scotia

[morgynm]

Oh and yes, boondocking when camping. Money is going in to the basics first so no solar yet. I've been hooked up to shore power (did I say that correct?) where it's parked at my Dad's.


Morgyn
1981 13' Boler
Nova Scotia

[RogerDat]

Originally Posted by morgynm

I'm lost! Got that the numbers just indicate the size but you lost me on the amp hours.

Here's the battery I'm looking at:
Group 24 AGM Deep Cycle Battery | Canadian Tire

It says 75 amp hours. We only camp on the weekends at this point in our lives so this will do for now?

And what is the difference between having one 12v vs two 6v? I've seen the 6v mentioned in other threads so I've been very curious!




Morgyn
1981 13' Boler
Nova Scotia

Amp hour = enough capacity to power 1 amp draw for 1 hour. BUT (you knew it was not going to be that simple! Right?)

12 watts @ 12 volts is 1 amp (if I'm wrong an electrical engineer or electrician will correct and scold me soon)

"All deep cycle batteries are classified and rated in amp-hours. Amp-hours is the term used to describe a standardized rate of discharge measuring current relative to time. It is calculated by multiplying amps and hours. The generally accepted rating time period for most manufacturers is 20 hours. This means that the battery will provide the rated amperage for about 20 hours until it is down to 10.5 volts or completely dead. Some battery manufacturers will use 100 hours as the standard to make them look better, yet it can be useful in long-term backup calculations. "

You don't want to draw a deep cycle below 50% charge so right there you throw out half of the stated capacity. Really shortens life of the battery to be run below 50% charge.

The actual amount of load matters too. In theory a 10 amp draw for one hour is the same as 1 amp draw for ten hours but the ten amp draw would drain your battery in less time than would be expected. High demand will accelerate the rate your battery drains as compared to a smaller demand.

Best suggestion to answer question of "is this battery enough" is to figure out what you will be running off the battery. And how long it will be running. Then take it's power draw times how long it will run to determine how much 12 volt you will use each day. Sound harder than it is.

As an example using made up numbers:
Lights @ 1 amp for 3 hrs. = 3 amp hours.
Water pump @ 4 amps for 30 minutes = 2 amp hours.
Television & Satellite ?
Fan ?
Laptop ?
Fridge ?

Just total all the stuff up that you use and you will know what you use per day. That answers the question how many days will this size battery provide that many amp hours while not draining below 50%

Lights are typically your biggest draw. Unless you have LED lights. Water pump draw is fairly high but only on for brief periods unless you have/use the shower.

My own guess is a bit of light in the evening getting ready for bed, toilet and sink use you would make it through two nights maybe three. With LED lights I would say for sure. TV & stereo, or vent fan gets less certain without knowing the expected draw (amps) and duration (time).

[morgynm]

No bathroom or water pump (although it's on my list for the future).

Forgot to say about the fridge... I don't think it runs on 12v anymore. The back doesn't look like it does in the dometic 211 manual. It only has a toggle on off switch, has to be plugged into an AC outlet conveniently placed in the same compartment and had (notice the past tense... because it scared the daylights out of me) the propane control valve screwed in the open position. So no fridge for us unless on propane while camping.


Morgyn
1981 13' Boler
Nova Scotia

[Jack L]

In addition to physical size and power you need to consider weight.

Here are some approximateweights for lead acid battery's. There will be some variation here.

Group 24 46 pounds
Group 27 55 pounds
Group 31 75 pounds
GC 2 6 volt 60 pounds X 2 to get 12 volts = 120 pounds

I would love to have 2 GC2 battery's but adding the weight to the tongue makes it impossible on the Bigfoot

[morgynm]

I figured the larger the group number would mean larger size/weight. I need to keep the Boler as light as possible. I forgot how heavy batteries were! Which is really funny considering I used to work in an auto department way back when. Tires and batteries were moved by whoever drew the short straw!


Morgyn
1981 13' Boler
Nova Scotia

[Carol H]

Originally Posted by morgynm

I'm lost! Got that the numbers just indicate the size but you lost me on the amp hours.

Here's the battery I'm looking at:
Group 24 AGM Deep Cycle Battery | Canadian Tire

It says 75 amp hours. We only camp on the weekends at this point in our lives so this will do for now?

And what is the difference between having one 12v vs two 6v? I've seen the 6v mentioned in other threads so I've been very curious!




Morgyn
1981 13' Boler
Nova Scotia

Morgyn as you plan to boom dock and use your power fan etc I would seriously consider going with the Group 27 over the group 24 . Check the prices at Costco if you have one near you - their battery prices are normally cheaper than Canadian Tire.

[morgynm]

I'll check them out tomorrow for prices! Thanks for the tip.


Morgyn
1981 13' Boler
Nova Scotia

[RogerDat]

Not a lot of price difference between 24/27 group but you are picking up ~20 amp hours so it is probably worth it if the larger battery will fit in the location.

If you ever go solar that "extra" storage capacity will come in handy if it is not sunny for a couple of days. Or even just figuring an extra 8 - 10 hrs. of running that fan if it's hot.

I know an earlier post mentioned that a pair of 6 volts (being 120 lbs. of battery) will have a lot of amp hours. 120 lbs. of 12 volt would be pretty close to the same. However 6 volt batteries for golf carts etc. are "true" deep cycle batteries, designed to withstand deeper discharge better than "marine" or dual use starting/deep cycle. True deep cycle also tend to do better at sustained load. If you need 225 ah it will certainly provide it. With one weakness if either battery malfunctions you don't have 12 volts. Which is why some earlier posts mentioned going to dual 12 volt batteries. Slightly less amp hours but either battery can run the system on it's own, just with less capacity.