New batteries

[MrNoodly]

Battery chemistry appears to have become a religious issue.

Yeah, it reminds me of the flooded vs AGM or two 6V vs one 12V debates from a few years back.

 

[PlethoraOfGuns]

Children, lets be civil here. Opinions may vary, but lets all be calm and try to understand things. I don't claim to be a master of this subject, but I did some research. If I'm incorrect, please correct me.

For one, if we're going to compare things, we're not going to compare the cheapest AGM to the most expensive LiFePo4. That said, I looked on Amazon for the cheapest of both. The cheapest AGM happens to be the Universal 100ah, at $180. The cheapest LiFePo4 is the BTR Power 100ah, at $310. For comparing, we're going to cycle the AGM down to 50% and the LiFePo4 down to 0%. Because of this, we'll need two of the AGM batteries to get the same useable ah capacity of the one LiFePo4 battery. So now we've spent $360 on AGM, and $310 on LiFePo4 for the same 100ah of battery capacity.

But what about cycles? Everyone cycles their batteries differently, so lets not use the whole "mine lasted me this many years" spiel. I'll give the benefit of the doubt and say the AGM will be good for 1000 cycles. Worst case, we'll say the LiFePo4 will be good for 3000 cycles. So now to get the same life cycles as the LiFePo4, we'll need to buy the AGM batteries three times. That's all if the LiFePo4 magic will hold true to the science and was properly taken care of. Most people don't cycle their LiFePo4 batteries down to 0%, so they'll definitely get many more cycles. So now we've spent $1080 on AGM for the same battery capacity as the $310 in LiFePo4.

But there are hidden things about LiFePo4 they don't tell you up front. I don't think off gassing is an issue. If your LiFePo4 batteries are off gassing, I'm pretty sure you want to run far away! One annoying thing is they won't charge below freezing. They also need special charging. You can't just charge right off the alternator of the engine, the LiFePo4 battery will absorb so much power that the alternator will get burnt up. But at the same time, LiFePo4 don't suffer from the peukert effect. So now you need a dc to dc charger. Bam, another $250. Most modern solar charge controllers have settings for LiFePo4, it can't be all that difficult to adjust the settings. So now we're at $1080 on AGM and $560 on LiFePo4.

My point is that when I saw the prices originally paid for the AGM batteries in this thread, I thought the LiFePo4 wasn't that far off in price. Someone please check my math. This is my thinking as I just switched from lead acid to LiFePo4 this past year. LiFePo4 aren't $2800 anymore like they were 5 years ago. I really do think it's worth it now to make the switch and not break the bank.

 

[Calaverasgrande]

From my understanding previous generation Lithium Ion is more likely to out-gas than Lithium Iron Phosphate.
My bank is connected to a MPPT DCDC charge controller, located inside a covered box in the most insulated part of my van. Doubtful it will ever get warm enough or experience a voltage condition that would cause that.
That all said, I did happen to have the money to afford LiFePo4 batteries at the time. And as said I got a deal on the Renogy batteries.
Otherwise I would have gone with AGM and just been extra detail oriented about making the battery bank a sealed box.

If anyone else is interested in Renogy gear. Check out their website, then go search on Ebay for the product you are interested in. They have all kinds of deals on Ebay. From brand new to open box and refurbished. I saved a couple hundred on my batteries.
By the way the Bluetooth batteries are cheaper than the heated LiFePo4 or the models with the RJ45 jacks to connect to a display. You just have to use an app to monitor the status.

 

[MrNoodly]

All the benefits aside, PlethoraOfGuns, if one can't afford LiFePo at the time you need batteries, it doesn't matter what the long term savings are.

 

[Tom_M]

I have a Renogy 170ah lithium that I installed 2 years ago. The only thing I did was I upgraded my solar charge controller. I have had no problems charging directly from my alternator or from my stock converter.

 

[PlethoraOfGuns]

There are advantages and disadvantages to any and all types of battery banks. If you already have a charge controller that does LiFePo4, and all you need to buy is the battery, it's comparable price to AGM. Technically the LiFePo4 will cost $50 less at the initial time of purchase. I just don't think people should ignore LiFePo4 as an affordable option.

 

[PlethoraOfGuns]

I have a Renogy 170ah lithium that I installed 2 years ago. The only thing I did was I upgraded my solar charge controller. I have had no problems charging directly from my alternator or from my stock converter.

I'm curious how this is possible. Everywhere I read states that the draw will be too great for the alternator and that a DC to DC charger is needed to limit the amount of power that is transfered to the LiFePo4 battery.

 

[Freelander]

I'm curious how this is possible. Everywhere I read states that the draw will be too great for the alternator and that a DC to DC charger is needed to limit the amount of power that is transfered to the LiFePo4 battery.

 BB says that each battery will draw unto 50 amp each when charging from the Alternator, that is why I bought the BIM and installed it.

 

[PlethoraOfGuns]

Ok, well it's still limiting the charge amount. I'm sure if you hooked up alternator right to LiFePo4 battery bad things will happen. What advanges do you have with a BIM over a DC to DC charger?

 

[ldsreliance]

Lithium-Ion refers to a class of battery chemistries that utilize lithium for ion exchange: LCO, LMO, LFP, NMC, NCA, LTO.  LiFePO4 is currently the most stable.

Lithium starts to outgas at 60ºC (140ºF).  A vehicle sitting in the Arizona sun in July can exceed 60ºC.  A black dashboard in the sun has been measured at 90ºC.
Overcharging or cell imbalance can also raise a cell temperature to over 60ºC.
Outgassing will bulge and eventually rupture the cell.

A corollary to Murphy's Law states: "All fail-safe systems fail, usually at the most inopportune time."

  
I'm well aware that LFP is a sub-class of Lithium Ion and I stated as much.  But even the chemistry that we normally associate with the term Lithium Ion does not emit gases except prior to and during a thermal runaway event.  Simply sitting in a hot car at 140F isn't a problem.  Runaway doesn't start to occur until 130-200C, which is almost double the temperature you specified.

Not only that, but you completely ignored the fact that the batteries referred to in this thread all have a BMS, which protects against over temperature.  AND 99% of the batteries referred to are LFP which does not emit anything under any recorded conditions that I can find, including thermal runaway, which is almost impossible to occur.

Please cite some sources if you have evidence contrary.  Otherwise, please stop spreading misinformation to people who don't know any better.

 

[Freelander]

Ok, well it's still limiting the charge amount. I'm sure if you hooked up alternator right to LiFePo4 battery bad things will happen. What advanges do you have with a BIM over a DC to DC charger?

The BIM allows 2 way charging, the Alt will charge the house batteries and the solar/shore power will charge the starting battery. I don't have to worry my starting battery going dead.

The BIM will cycle on for 15 mins and off for 20 to charge the house, and will cycle on for 1 hour and off for 2 minutes to charge the starting batteries, this is determined by the state of charge on both sets of batteries.

 

[jacqueg]

Interesting discussion.

For my part, when it came time to buy a battery, I went with the cheapest LiFePo4 I could find. It only has a five-year guarantee, but I bought it from a vendor in QSite, who will likely be there when the time comes - if it ever does. Cost $600 IIRC. I am sure it is not as well built as one of the name brands. But for me, the deciding factor was my V6 engine. The LiFePo4 has it all over the other choices in terms of weight.

 

[Calaverasgrande]

I got 2 Renogy 100AH BT batteries hooked up to a Renogy 50 amp DC-DC charge controller.
It only pulls 25 amps off the alternator, the other 25 is supposed to come from solar.
I figure that will work great for me as an incremental solution.
If I go past 2 panels I'll upgrade to a charger with more headroom on the amps side (and maybe that can handle higher volts as well).
Already eyeing another pair of Lifepo4 cells to increase my capacity to 400AH.
As it stands I can run my fridge, lights and computer for about 2 days no sweat. But if I turn on a tiny space heater I only get a couple hours!
I could get a fueled heater, but then I have to worry about ventilation etc.
So I just use the space heater when changing in the morning or to take the bite out of the air at night. My bedding is more than enough down to the 30's.
The BM built in to the cells and the charge controller slows down the charge as it nears full. And stops when it is full. I did install 300amp switches and 60 amp fuses between the batteries charger and alternator. I cut them out when not running just to be safe.
I'm pretty sure I'm good only drawing 25 amps off the alternator. But keeping an eye (and nose) on it.

 

[1shemp]

Best to buy the cheapest fla batteries.

 

[skyl4rk]

What do you think about combining lead and lithium batteries together in one battery bank?

Video about adding a lifepo battery to a large lead acid battery bank:

 

[PlethoraOfGuns]

Whoa, that's crazy that guy does that. Very cool concept. I suppose he is right, but still sounds scary to me. I only have room for two batteries, so not going to ever attempt combining a lead acid and lithium battery bank. Does anyone else have experience or opinions on this?

 

[Freelander]

What do you think about combining lead and lithium batteries together in one battery bank?

Video about adding a lifepo battery to a large lead acid battery bank:

I wouldn't do it, the 2 battery type have totally different charge profiles, and use different chargers.
The FLA use a 3 stage charger and a Lithium uses a 2 stage charger.

 

[Spaceman Spiff]

What do you think about combining lead and lithium batteries together in one battery bank?

Lead acid 12V batteries have a fully charged resting voltage of 12.6 - 12.8
12V Lithium batteries have a fully charged resting voltage of 13.3 - 13.4.
The lithium battery would be constantly trying to bring the lead acid battery up to 13.3 volts until it dropped down to the LA voltage (12.8V is about 17% charged for li-ion batteries).

 

[skyl4rk]

Here are the problems I see with the lithium plus lead battery system:

When the two types of batteries are connected, there will be an initial inrush current as the lithium battery tries to bring the lead battery up to its voltage level. In order to prevent hot components, a power resistor should be used until the battery voltages balance out. This could be a problem because of human error, it would be easy to make a mistake and connect the batteries without balancing them.

If the BMS of the lithium battery disconnects the lithium battery from the system, the same inrush current problem could occur when the BMS reconnects the lithium battery to the system.

If a lead battery cell went bad, the lithium battery might dump its power into the bad cell causing heat damage to wiring, connectors, switches and lead battery.

Some type of current limiter is needed to avoid burning out the alternator when charging lithium. This is fairly easy to overcome by using a charge controller designed for lithium.

The lithium battery will constantly be providing power to the lead battery to keep it at float voltage. So there is some power loss using this method. How much, I don't know.

I don't recommend this system, I am just trying to learn about it because it seems it might have some advantages if it worked.

 

[frater secessus]

Everywhere I read states that the draw will be too great for the alternator and that a DC to DC charger is needed to limit the amount of power that is transfered to the LiFePo4 battery.

My mentor used to say "in theory, theory and practice are the same. In practice, they are not".

my testing​

My RebelBatteries 100Ah LFP charges at ~30A from an isolator (180A alternator). This is actually less than the previous bank, 220Ah flooded lead-acid bank that pulled ~42A at 50% DoD. Both the current and voltage are within the Li battery mfg charging specs.

To be fair, if somebody gave me a 20A DC-DC charger I would absolutely use it as I would prefer to charge Li at that slightly gentler rate and lower voltage. Until then I will use the isolator.

Battle Born's take​

Let's revisit Battle Born's statements in their alternator charging video. I will add emphasis to point out the most interesting bits.

• 0:12 - "Can I use my alternator to charge the batteries? The answer is yes, you can. Under most circumstances you don't even need to modify your system"
• 0:23 - "...If you have a system that is bigger than three battery banks you're going to want to use our special battery isolation manager..." (link to their product listing added)
• 1:20 "If you have three or less batteries you can still use the BIM but you really don't need it, you can just use a standard isolator."

Note that I am not telling people to isolator charge LiFePO4 with wild disregard or without understanding the issues. I am saying that the industry leader explicitly allows it, and that isolator charging works nicely in my setup.