Battery question

[Twistedlarch]

Hi all, brand new to the forum and travel trailers! 🙂

I'm going to start my 1st post with a battery question:

I have 2 group 29 batteries that I plan to run together, any idea what I'm looking at for battery life for a 21 ft trailer during your average normal use? I plan to occasionally run a TV and DVD player for the kids (approximately 200 watts) with a 1500 watt inverter.


Thanks
Brian

[wa8yxm]

Some numbers and it's all about the numbers.

A group 29 MARINE/deep cycle (or just about any G-29 save Optima) is just over 100 Amp hours. about 20-25 usable before you damage the battery So you have about 40-50 Amp Hours of usable power
200 watts is about 20 amps by the time the inverter converts it.. But you likely won´t be using that much.

NOw a pair of GC-2 (Taller but you would need to shim them some side wise) hold 220 amp hours (About the same total amp hours) but you can use half or 110 of those because those are DEEP CYCLE batteris. that? over twice the usable watts. and a smaller price tag in most cases.

[opnspaces]

Hey you made it through the weekend, that's what counts. 🙂

[Twistedlarch]

First Dry trip completed last week, we arrived Thursday afternoon and checked out Monday morning. My refurbished group 24's (Interstate Econo Power) made it till Sunday morning when I noticed the voltage went down to 11.9. The kiddo's watched a movie every night and we had to run the heat at night, temps got down to high 30's. Swapped out the 24's to the 29's early Sunday morning.


Thanks!
Brian

[Twistedlarch]

DrewE wrote:
If this is a modern TV, it and a DVD player will use a lot less than 200W in practice, quite likely less than 100W. It does depend somewhat on the size of the television set; larger ones have bigger backlights, which is probably the biggest user of power in the TV.

The size of the inverter is of little importance so long as it is sufficient for your load.

In many of these sorts of situations, and particularly with batteries that are not new and have somewhat unknown histories, the best way to figure what sort of life you'll see is with an actual trial. Certainly some rough estimates can be made with reasonable assumptions, but empirical evidence trumps that every time.

Just purchased a watt meter. The 24" flat panel and DVD with all the lights on in the trailer measured at 152 watts. The microwave bumped it up to 1300 watts.


Thanks
Brian

[wa8yxm]

Twistedlarch wrote:
IMy group 29's are both Interstate RV/Marine batteries that I got a few years back for our Pop up trailer. We did 3-4 four day camping trips every Summer, the batteries held up great, I think the lowest they got was 75%.

With MARINE/deep cycle that is the key to long life. Never let 'em get below 75 percent or so (80 is even better)

True Deep Cycle (like the GC-2 class both I and one other recommend)
can go to half full before rapid aging sets in..

Someone said 4-5 years. MY oem GC-2 lasted 9 and my Deka G-20's went 4 years before I even needed to water them (DISTILLED ONLY) so you can see why I like quality GC-2's

What's better.. Well there is a thread about LI batteries (or two) and those are looking.. more and more .. Interesting.. I"m hoping by the time my G-20's need replacement (230 amp hour GC-2 class) LI's will be more competitive.

[DrewE]

If this is a modern TV, it and a DVD player will use a lot less than 200W in practice, quite likely less than 100W. It does depend somewhat on the size of the television set; larger ones have bigger backlights, which is probably the biggest user of power in the TV.

The size of the inverter is of little importance so long as it is sufficient for your load.

In many of these sorts of situations, and particularly with batteries that are not new and have somewhat unknown histories, the best way to figure what sort of life you'll see is with an actual trial. Certainly some rough estimates can be made with reasonable assumptions, but empirical evidence trumps that every time.

[Twistedlarch]

I do have a 1500 inverter but only plan to use it for the TV & DVD player (roughly 200 w together).

I also have 2 much smaller batteries that came with the trailer, they are refurbished interstate 12v's (Interstate Econo power). I have no idea what group they are, all info decals have been removed.


My group 29's are both Interstate RV/Marine batteries that I got a few years back for our Pop up trailer. We did 3-4 four day camping trips every Summer, the batteries held up great, I think the lowest they got was 75%.


Every Fall I remove the batteries from the trailer and keep them on a float charger on my work bench in the garage with caps loosened.


Again, I do have a 1500 watt inverter but I do not plan to use anymore than about 500 watt max.

[time2roll]

Generally you should get 4 to 6 years from those batteries if they are properly maintained. Need to get a proper charge, don't over discharge them, mind the water level, store them properly. Sounds easy but has proven difficult for many RVs.

How are you charging these batteries? If it is a WFCO converter you already have a strike against you.

[theoldwizard1]

Start with your load (200W). Watts is basically volts time amps (close enough) so that is about 2A @ 120VAC. Assume about a 20% loss in the inverter (yes, that number is high) so multiply by 1.2 (2.4A). 120VAC is ten times 12VDC so if we have 1 tenth the volts we need ten times the amps (24A).

Most batteries will have a "reserve capacity" rating which is the number of minutes you can draw 25A and not drop below 10.5VDC (your inverter will probably shut off before then).

A Group 29 has about 200 minutes of reserve capacity. You have 2 batteries so IN THEORY you should get about 400 minutes.


These are very rough numbers but they should bet you "in the neighborhood"

[pianotuna]

Are the group 29 marine batteries or are they deep cycle?

The inverter is on the large side for what you wish to use it for. What is the idle current draw?

[pianotuna]

.

[twodownzero]

I second the GC2 battery comment. Start with two and that'll probably be all you need. I have four and while I'm all set for cloudy days, I could probably get by with two. I don't have a tv or a 1500 watt inverter though.

[wa8yxm]

Two Group 29's (right around 200 amp hours and you can safely use about 40 of 'em) should work with a 1500 watt inverter 3 would be better but it's more a factor of load and you are under 1000 watts load (closer to 500) so should not be a problem (200 amp hours per 1000 watts of inverter is Xantrex's suggestion) I think you will be OK.

Now if you already have the batteries.. OK
When you get around to replacing them consider GC-2 golf car batteries These are six volt so you hook 'em in series to make one BIG (4d big) 12 volt battery
Around 220 amp horus and you can safely use half (Note the difference you went from 40 usable to 110 nearly 3 times the usable power)

They may need to be "Shimmed" a bit to fit in a group 27 box and they are Taller so measure before you upgrade.

They also need to be watered from time to time (DISTILLED ONLY)

They may also cost less than a pair of 29's

But as I said. if you already have the 29's they should be good till they fail (NOTE folks. all batteries fail sooner or later)

Make sure you have a good 3-stage converter to charge 'em with. I like the Progressive Dynamic Charge Wizard controlled units... Have yet to find one better.

[gbopp]

Welcome to the forum. Have you ever read The 12 Volt Side of Life?
It may be helpful.
Enjoy your travels.