Lithium vs Lead Acid: a Basic Comparison

[peteco]

I have been on the sidelines regarding battery upgrade to Lithium due to cost for now. There has been much discussion on this forum but I quickly get lost in the details. But I just read this article and was astonished at the performance advantage of Lithium shown here. I am surprised the lead acid only show half their “rated” capacity as being available to use; only ~100Ah (at 10 amp discharge) for two 235Ah 6v batteries. Even worse for higher amp discharge. I realize there is more to the lithium vs lead acid story, but this difference is astounding.

I like the way Battleborn has presented the results. But are these results truly representative or has Battleborn fudged something here or left out important information?

https://battlebornbatteries.com/comp...teries-series/

[@Michael]

Here's what I found interesting about that article:

What is clear from the curves in Figure 2 is that the relative performance is highly sensitive to the discharge rate of the batteries. At a 50 A discharge rate, the BB10012 can sustain above the 11.8 V cutoff for almost 2 hours, whereas the GC2 batteries cutout in less than an hour. At the lowest discharge rate, the BB10012 can deliver 10 A for around 9.5 hours, whereas the GC2 batteries last for over almost 12 hours.

If you are OK with a deep discharge, the lead acid's do quite well against lithium.

I was interested in the fast recharge aspect of the lithiums as much as the useable capacity. They charge faster so solar, generator and alternator run times are minimized.

[markopolo]

The 11.8V cut-off is very high SLIGC115 pair for the 50A discharge test. It's an unfair comparison IMO.

Additionally, the SLIGC115 pair should have been cycled a few times prior to testing.

For lead acid batteries, a 10.5V cut-off under a 50A load would be more representative of real world use.

[peteco]

Originally Posted by markopolo

The 11.8V cut-off is very high SLIGC115 pair for the 50A discharge test. It's an unfair comparison IMO.

Additionally, the SLIGC115 pair should have been cycled a few times prior to testing.

For lead acid batteries, a 10.5V cut-off under a 50A load would be more representative of real world use.

But can you operate anything that has drawn the battery to 10.5v?

[markopolo]

10.5V under load is not unexpected for lead acid batteries.

It is a common cut off point associated with inverter use. The 50A load is not a typical/commonly seen long duration DC load. A 50A load would be seen if running a small coffee maker or something similar on an inverter.

The popular BD35/50F DC compressor unit used in fridges can be setup with a 9.6V cut-out. The standard cut-out for the BD35/50F is 10.4V.

I'd guess that there was approx 100Ah usable capacity left in the SLIGC115 pair after the 50A 11.8V cut off test. Probably another day of DC compressor fridge use along with other light use.

[booster]

Originally Posted by peteco

But can you operate anything that has drawn the battery to 10.5v?

I have mentioned several times in the past that I thought the Battleborn comparisons were severely biased and deceptive. The original life calculations were even incorrect. The 50% bottom for lead acid is, as we have discussed a few times, not correct IMO. The world doesn't end at 49% and the costs of going lower are really quite small.


Battleborn batteries may be just fine, but the way the push them makes it look like they are infomercial hucksters to me. Drop them in a go they say, basically, but I really doubt the would work out well for many people over time, but we will see on that.


Personally, the downsides of lithium are still too large for us, and our AGM bank is working very well for everything we need and then some. If they died tomorrow, I would replace with the same.


10.5v is essentially empty for an AGM so I wouldn't go there, but 80% is not a problem for me and all but the very high amp, voltage sensitive, stuff will run down to that point.

[markopolo]

With lead acid batteries, it's important to distinguish between at rest voltages and under load voltages.

10.5V at rest is a depleted lead acid battery. 10.5V under a 50A load is completely different.

In the linked 50A 11.8V cut-off test, Battle Born reported that 40Ah was drawn from the 230Ah batteries. The article kind of leaves the impression, in my opinion, that the battery was unusable after that.

In fact, there would have been a lot of capacity left. If there's any doubt then look at the Reserve Capacity of the SLIGC115 battery: https://www.batteriesplus.com/produc...ultra/sligc115

It is rated to be able to supply 75A for 115 minutes. That's much greater than the the 50A for 50 minutes or so that Battle Born reported.

[JohnnyCLE]

This is an informative article on the state of Lithium batteries.

https://marinehowto.com/lifepo4-batteries-on-boats/

The considerations for capturing a trickle of solar and running light 12v demands are different than those for ripping 110v current for heavy appliances. Build quality matters as much as chemistry.

Fortunately what is available today is much different than what was available 3 years ago and, I have to imagine, what will be available 3 years from now will change the equation even more.

There may also be better AGM solutions from Silicon Joule technology.

https://www.gridtential.com/silicon-joule

[hbn7hj]

I have two RVs with both types of batteries. The lithium is always used when using an inverter. The FLA is only charged from the generator while the lithium is being charged. When the lithium is full and limited solar has not charged the FLA to full then the lithium is used to charge the FLA. Another 10 minute generator run will recharge the lithium.

Both battery banks at 100% at sunset. If I don’t need the FLA capacity I prefer to use only the lithium as it charges so much faster. While driving the alternator is switched to the FLA.

Lithium is certainly the “friendlier” battery. It is inside so the furnace keeps it warm and winter stored in Phoenix with the furnace turned on if necessary.

The system works so well I plug friends coaches into my inverter so I don’t have to listen to their generators. I have not installed a Danfoss refrigerator yet. I might not be so generous with the power when that happens.

[JohnnyCLE]

This has a lot of intuitive appeal and sadly reflects the reality that both chemistries need coddling. AGMs need coddling in their charging profile while LIs need environmental coddling.

Sacrificing precious internal space for one LI to work in conjunction with one or more AGMs allows each to focus on what it does best - friendlier charging / discharging profile vs lower cost volume storage placed in a less protected location. It does seem that LIs are much more forgiving to the vagaries of solar and can be used to better smooth the charging to the AGMs.

The issues of if and how to add LI smartly to an AGM based RV, without having to replace everything, are interesting and different than those of a new build or 100% conversion. Starting with just solar to lithium and then lithium to AGM would allow a mixing of 12v and 6v/24v profiles. An added benefit in my case would be potentially eliminating a midpoint 12v tap.