Batteries

[Socal Tom]

This thread has gotten me to re-think my battery decision or to at least make double sure of my decision.

For the typical weekend warrior the occasional dip down to 20 or 25% probably won’t make a difference.

For the sake of discussion, lets say your trailer will not only see the life of a "weekend warrior", but will be on the road for a month at a time, maybe even longer.... and maybe twice a year. And let's also say there are numerous week+ plus long trips. So more than weekend get aways. And given this usage if one didn't really want to have to always be concerned about whether their battery was going to hold up or be concerned about running it below the threshold (define that as you may)..... would a lithium make sense?

Thanks

John

It would depend on a couple of things
1) The most important question is "How much reserve power do you have?" ( In my case a 100AH battery would have about 1250 watt hours max capacity, at 50% I have 625 to play with, I use about 250 per day ( assuming no solar) so I can go about 2 days with no sun before I drop below 50%, the third day with no sun gets me into the yellow zone, a 4th day would be bad.

2) How quickly can I recharge?
My solar setup makes about 450watt hours on a sunny day. So if I go 2 days with no charging, I can make it up in one sunny day.

3) How frequent are days with no sun? I'm in So California, so I rarely have 2 days with no sun . So the probability that I need to go 3 days and take it down to 25% would be low ( and there are things I can do to conserve if that happens).

4)- Since my battery is lead acid, I can use TV charging in a pinch. Its not fast, but it does work. I've tested it with my Baylite meters and the charging I get provides enough power to power my 12V fridge and put 6 to 10 watt hours back into the battery per hour.( which is about the same as the standard 120V battery charger). I'm assuming if you are going on the road for a month it means driving frequently, so if you are without sun, you can at least reduce the load on your battery while driving.


So for me to justify a lithium battery, It would probably be about size and weight.

Lets say that I used more like 500 watt hours per day. Then I would only have 1 day reserve power, so 1 day without sun would get me near 50%. If I expected to be without solar charging for more than one day frequently, then I need more battery capacity. If I set my reserve power at 1000 watt hours, ( 2 days reserve ) then with Lead acid I would want about 160 AH of battery capacity. But I didnt have space or the weight was important, then with LIPO you could get by with a 100AH battery ( assuming 13V nominal and 30% min charge). But the LIPO reserve is a hard cut off. If you go 2 days without sun, you are out of power. With the lead acid, the 50% is a soft cut off, you can still go lower if you need to .

It seem's like your real concern is worrying about the state of charge on your battery. Here is my suggestion. Install some kind of battery monitor like the Baylites https://www.amazon.com/bayite-6-5-100V- ... B013PKYILS
I'm sure there are better ones, but I have 2 of these. One monitors power in one monitors power out. You can set alarms ( just flashing, no sound) . I have mine set at 12.2 volts ( roughly 50% for a lead acid battery). Then most of my power goes through my solar charger, which will cutoff power if voltage goes below 11.9 about 40%.( fridge doesn't go through here, but has a built in voltage cut off). If the flashing alarm goes off, then I make sure we aren't wasting power and I verify the solar is working properly, and I will set up TV charging if necessary.( I carry jumper cables, so I can always hook the cables between the TV and the battery directly to speed the charging). For short trips If this occurs I'm probably packing up to go home anyhow.
If for some reason I don't notice the flashing alarm, then when the lights stop working at 40% I notice for sure.

However, what really happens.
Once you put in the Baylite meters, you start watching them. ( hourly or less). You realize that when the sun is up your battery voltage stays above 12.4 almost constantly, and that during the night you use very little power ( except the nights I hook up a portable video projector), and when you wake up the power is still 12.3 or higher. I never get below 20% with my battery on a sunny day.

I think in your case, if you were on the road for a month, you would probably spend at least sometime in camp sites with power ( and showers), which also gives the option for plugging in and charging.

So in the end, for a towed trailer I think the easiest option is lead acid, it can be charged by the TV easily and the 50% cut off is a soft cutoff, vs a hard cutoff for LIPo. However, it size and weight are more important than cost, then LIPO makes sense, but I would include the ability to charge with my TV if I'm really concerned about not having enough sunny days.

[Graniterich]

Even a lead bank can go well over a dozen years, but up-front expensive banks are only justified for those with higher Ah per day needs, and using them many cycles every month.

In that case then they work out cheaper per year, but it does take the right gear and knowledge to get that value back.

My 35 Amp sla is six years old, light use a few times a year, I use a battery tender float charger when stored. I keep wondering how long it can go. Twelve years sounds good to me

[John61CT]

LOL I didn't mean any lead batt!

Usually EoL in industry is 80% capacity remaining, but consumers often push to 70% or lower.

Best if mission critical to replace before signs of wear become apparent, or at least keep a close eye.

With such a cheap unit personally I'd just do so every 3 years.

[western traveler]

Well heck,
Now I am questioning my battery plan. I have a Honda 2000 that in the past when boondocking (most often with no neighbors in the vicinity) I had used to bring my LA batteries up. I am not ready to do solar but it is in the near future.

My battery for this build is going into the rear galley. So if I use LA as planned I was thinking I would need ventilation in its location.

I want to be able to run my Propex 2000 heater without concern. As to the rest of 12v usage it would be a cabin light or 3 and charging phones and iPads. We don’t do TV/videos etc while camping.

Looking at AGM batteries I could eliminate more holes in the floor for air to the battery.
I don’t know if someone had a typo or not. Is cold weather a problem with these batteries?

Would 150ah be a satisfactory cushion that I wouldn’t have to baby it constantly. Yes, battery monitor etc.

With our former trailer and 2 6v golf cart batteries there were winter days that they got charged with the Gen daily. I would love to avoid that.

[Socal Tom]

Would 150ah be a satisfactory cushion that I wouldn’t have to baby it constantly. Yes, battery monitor etc.

t.

Can’t tell you with out knowing how much power you will use.

[Capebuild]

SocialTom, Thanks very much for your informative post. A lot to digest and need to read it over a few times. But thank you very much for your thoughts. I do have a Victron BMV712 batt monitor I'm going to use so whatever battery I wind up with, that will help keep track. I've started to rethink the AGM (but will probably still go with LifePo)... comparing a 100 Ah Battelborn with a 110 Ah FullRiver AGM. They both seem to have similar footprints so the batt box I've got built could accommodate either. The FR is twice the weight of the BB and 1/2 as much $$.

John

[Graniterich]

LOL I didn't mean any lead batt!

Usually EoL in industry is 80% capacity remaining, but consumers often push to 70% or lower.

Best if mission critical to replace before signs of wear become apparent, or at least keep a close eye.

With such a cheap unit personally I'd just do so every 3 years.

I can dream! Not mission critical in my teardrop, can wire a jackery in if needed. But the jackery powers down after a few hours if no draw not good at night.

[Socal Tom]

SocialTom, Thanks very much for your informative post. A lot to digest and need to read it over a few times. But thank you very much for your thoughts. I do have a Victron BMV712 batt monitor I'm going to use so whatever battery I wind up with, that will help keep track. I've started to rethink the AGM (but will probably still go with LifePo)... comparing a 100 Ah Battelborn with a 110 Ah FullRiver AGM. They both seem to have similar footprints so the batt box I've got built could accommodate either. The FR is twice the weight of the BB and 1/2 as much $$.

John

Glad to be of service. At the end of the day, we are all doing what we think is best, but its good to exchange ideas before we lock in on something.

[bdosborn]

<snip>

[bdosborn]

<snip>

[Socal Tom]

comparing a 100 Ah Battelborn with a 110 Ah FullRiver AGM. They both seem to have similar footprints so the batt box I've got built could accommodate either. The FR is twice the weight of the BB and 1/2 as much $$.

Make sure you look at the total cost of ownership and not just the first costs. Pretty amazing how much lower the cost is for LiFePo4 versus LA is in the long run. Here's a link that comes up with a quick web search.
https://relionbattery.com/blog/total-cost-ownership-lithium

Bruce

I think that is a good point Bruce, but in my case the FLA battery is $100. The replacements have been $100 and they get replaced every 5 years. It would take 20 years to break even with a lifepo. I probably won’t own my TD in 30 years. The article you posted is from the lifepo supplier, so it must be taken with a grain of salt.

[bdosborn]

<snip>

[Socal Tom]

Another thing that will be more relevant over the next few years is what type of battery you have in your TV. Right now with movst TVs the charging system is designed for FLA. charging a LIFePO would require a dc/DC charger. In a few years more TVs will use LIFePO and the opposite will be true.
Tom

[lfhoward]

I recently built a 156 Ah LiFePO4 for my trailer for much less than an off the shelf unit would cost. But I also had to upgrade my solar charge controllers and shore power battery charger to ones that can charge LiFePO4. That got kind of expensive. But I plan to keep my trailer pretty much forever, so the long term investment in my view is worth it. Performance-wise, it is night and day vs. the marine deep cycles I was running before.

[John61CT]

Another link for the coulomb counter, up to 350A shunt
https://a.aliexpress.com/_eMNZhx

For LFP to be better value from a strictly economic POV it has to actually last those decades

and all it takes is one catastrophe over that time, whether hardware failure or ignorance or inattention

or poorly made cells in the first place.

So the real justifications are the higher density, greater capacity usage, no need to get to Full

or the owner just likes learning the latest tech.

No model that requires decades for ROI makes sense from a purely economic POV.