Second Battery question

D

donks2

Member
Joined
May 2, 2018
Messages
28
Location
Grass Valley, CA
Greetings All, new to the forum and my first post. We have a 2001 Hawk that we got about 1.5 years ago and I'm making some changes, slow but sure.

I've been researching, read lots of old posts, but still unsure about my question.

We were on a trip to DV a couple of weeks ago, and our house battery died. We stopped into an RV place in Bishop and got a new battery. I believe it was the 3 way fridge that killed the old battery,(running on12v while traveling, but forgot to turn it off during a 2 hour stop). Only used propane after that, and have pulled the fridge out when we got home. At this point we have very little draw, just a fan and water pump.

We are replacing the old 3 way fridge with a TruckFridge TB51A, and I'm working out all the solar etc. Thanks to ski3pin for his great testing info!

I was going to put 2 6v in, but since we had to do an emergency replace, and they did not have any 6v, I now have one new 12v. Optima Bluetop AGM Marine duel purpose

I'd love thoughts on the best way to proceed.

Can I add a second 12v battery to this? It's dated 10/18 and was installed 3/05. The guys at the RV place thought it would be fine if we do it soon. Any Thoughts? If it's ok to do this, would it double our amp hours? (trying to wrap my head around solar planning!) The battery is rated C-20 capacity 55aH. According to ski3pin's tests, we can reasonably safely assume it will use about 15amp hours in 24 hours, so even the single battery should be ok for 3 days without charging? Am I understanding this correctly? I am electrically challenged! We will be adding solar, but that is a whole other kettle of fish in our old camper that is not pre wired.

Is it worth loosing the floor space to a second 12v? Expensive timing to go with 2 6v, but could be willing as I could use the 12v in my chicken coop hot wire solar set up when the battery that is out there dies. Or maybe run this till it dies and get the 2 6v then... decisions!

Thanks, this forum is just amazing!
 
Welcome to WTW!

The members here are a great source of information and knowledge and I’m sure someone will be along soon to provide you with a more detailed reccomend action.

I had 2, 6 volt (220 AH) batteries for several years. Due to an issue that was of my own doing I needed to replace the batteries and ended up getting one, 100AH Lithium Ion battery that is every bit as capable and in some ways superior to the 2 six volt set up.
They are expensive but should be very cost effective over their longer lifespan.
I can reccomend Battle Born batteries.
 
Welcome to WtW!

Your new 55AH battery is likely not a good long term solution. If you are right about using 15AH/day, you really only have about 2 days of capacity. How so? Unless you go with a LiFePo battery like Eddie suggests above, you are stuck with a lead acid battery like the one you already have. Their chemistry is such that the life expectancy decreases rapidly if they are discharged often below 50% of capacity. Meaning you have 28 AH of usable capacity. This graph/article explains this better than I can:
https://prismsolar.co.uk/shop/files/OffGridLiving/FLALifeSpanVsDOD.pdf?732711096

Another thing to keep in mind is temperature. A deeply discharged battery can be severely damaged in the cold, because it will freeze. A fully charged battery will not freeze.

That said, you could use your new battery "until it dies". How many days/nights a year will you be using it? When you get back from a 2 day trip, can you plug it in and charge it up? A simple NOCO Genius 7200 would be able to bring it back to full charge if you give it a few days.

I like being sure about how much capacity/draw I have in my rig, so I have a few gauges. A volt meter is not enough in most cases. A real battery monitor like the Victron BMV 712 is the current (pun intended) favorite recommended here by me and others.

As for installing solar, that is a bigger kettle of fish for sure. Ask away when you are ready for more!
 
Thanks for your replies! That is a helpful link for my understanding of . So, the idea of a second 12v... any thoughts on that, with our month old battery?
Does it double the amp hours, and more importantly, the usable amp hours? We will not be using the TruckFridge until we get our solar setup up and running.
 
This is probably not what you want to hear, but I would sell the Optima and (after doing your research) buy batteries that better serve your needs. The problem with Optimas is not the quality per se, it is their construction that leads to a much lower AH capacity for the same footprint than an AGM or flood cell. They are great for some use, but not as a house battery in an RV.

I found this out the hard way after the dealer recommended an Optima blue top as the aux battery in my Silverado. Later, on another RV forum, I learned about their lower AH capacity (around 55AH vs +/-80AH for a group 24 AGM).

IMHO, it is not worth living with a substandard battery in an important application like the house battery in an RV, especially one that is primarily used for boondocking like a FWC. There are many threads on batteries. I suggest researching what will best meet your needs, then selling the Optima while it is still "new" to help fund the new batteries.
 
Vic Harder said:
Yes, adding another 12V will give you more usable AH. Ideally you would want two identical batteries. 2*55=110. Still not a lot of AH, and easily obtainable in ONE battery of reasonable size.

On the solar question, check out these threads:
http://www.wanderthewest.com/forum/topic/13230-i-need-more-power-scotty/

http://www.wanderthewest.com/forum/topic/3887-ultimate-solar-thread/
Click to expand...
Thanks so much for these links. I've learned a lot! My searching the forums seems to have a bit to be desired, so it's great to get these links!
 
Trailbob said:
This is probably not what you want to hear, but I would sell the Optima and (after doing your research) buy batteries that better serve your needs. The problem with Optimas is not the quality per se, it is their construction that leads to a much lower AH capacity for the same footprint than an AGM or flood cell. They are great for some use, but not as a house battery in an RV.

I found this out the hard way after the dealer recommended an Optima blue top as the aux battery in my Silverado. Later, on another RV forum, I learned about their lower AH capacity (around 55AH vs +/-80AH for a group 24 AGM).

IMHO, it is not worth living with a substandard battery in an important application like the house battery in an RV, especially one that is primarily used for boondocking like a FWC. There are many threads on batteries. I suggest researching what will best meet your needs, then selling the Optima while it is still "new" to help fund the new batteries.
Click to expand...
We are coming to that exact conclusion, Trailbob, thanks for the back up! We would need to get 3 more of them. I'll search out the battery threads. We are in the process of figuring out what our power usage will be, then will size things from there.
 
Lots of good info here. The suggestion for first buying a Victron or Trimetric battery monitor is probably the best idea as from that point forward you will always have good information on the state of your batteries health.

Given that you have a use for the D34 Optima in the hen house, I would would seriously consider the Battleborn suggestion by Smlobx as a first choice rather than another small Bluetop.

Another thing not mentioned as often is the difference in charging profile between the AGM and LiFePo4 batteries. The AGM will be charged in bulk mode until about 80 % full, then it swithces to absorption mode where it charges much slower for several hours before it is fully charged. The LiFePo4 charges at the bulk rate until full and isn't as picky about being fully charged regularly.

Check with Battleborn support for any changes you may need to make in your shore power/ alternator charging systems and recommendations for solar..

Paul
 
Howdy Donks and nice to Emeet you.

We have gone off on an entirely different angle and now have our small portable refer run off the TRUCK battery.

We have a very small AGM battery in the camper for our lighting and will eventually hook up the Solar to charge it.

We recently traveled for a month and the little battery for lights never needed charging......

Running the Dometic portable in the camper but off the truck battery was a simple wiring issue.....

All said, we camp fairly simply and have no water pump or furnace fan.

David Graves
 
Thanks for all your helpful replies.

PaulT- thanks for the heads up about possible system changes with a LiFePo4, that is news to me. We are considering all options right now (except keeping the blue top!).
 
Thanks for your feed back. I think we will keep our truck battery just for truck starting... been stranded in the boonies with a dead battery once, that was enough for me! But love hearing all the different ways folks go about powering their 12v fridge.
Happy trails!

DavidGraves said:
Howdy Donks and nice to Emeet you.

We have gone off on an entirely different angle and now have our small portable refer run off the TRUCK battery.

We have a very small AGM battery in the camper for our lighting and will eventually hook up the Solar to charge it.

We recently traveled for a month and the little battery for lights never needed charging......

Running the Dometic portable in the camper but off the truck battery was a simple wiring issue.....

All said, we camp fairly simply and have no water pump or furnace fan.

David Graves
Click to expand...
 
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