Are Lithium RV Coach Batteries Expensive?

Here's a bottom line for a small RV system, using off the shelf lithium battery components. I'm editing this post to add the following which I think is a very important consideration:

AGM batteries 220Ah = 110Ah useable,
Lithium (LiFePO4) 200Ah = 160Ah useable,

In other words, a similarly rated lithium battery system will probably deliver about 45% more power than a similarly rated AGM battery system, and it will probably do so for at least 6-7 years. Now do I have your attention?

What I am planning is not a "build it in your basement" system comprised of battery packs assembled at home from hundreds of batteries. There are some serious considerations when using lithium batteries, which can be safe and environmentally superior to lead acid batteries. Those batteries do require monitoring and controls so that a cell failure can be managed. My concept system which will probably be built is comprised of pre-assembled batteries packs and off the shelf controllers and solar panels. This system is similar in design to current AGM coach battery systems:

Battery watts: 1200 (or 2400) (1.2-2.6 kWhr, replace 2-6V 220Ah AGM batteries)
Solar Panel = 140 Watts
Cycles: 2000 to 3000 at 70-80% discharge (DoD). Up to 5000 cycles possible. (See notes).
Self discharge = less than 3% per month.
Battery weight = 25 to 33 lbs.
Battery storage temperature limits = -20 to 114F
Battery operational temperature limits = 32 to 114F (some batteries are rated 5F to 115F).
Includes MPTT Solar Controller and 140 watt solar panel.
Includes 120V charger for lithium batteries.
Cost of entire system components: $1,690 - $2,600

Why the cost differences above? There are different technologies available. The most reliable are the most expensive. I think the lower number is realistic. After all, I won't be sailing my RV around Cape Horn. Note: Read the notes at the conclusion of this post for some important info that impact the specifications above.

Can I Get More Power?
The above can be "scaled up" with more batteries, larger solar panels, etc.  A 2400 watt (whr) system could cost about $3,000. The batteries would weigh about 60-65 lbs, which is about half of a similar AGM battery. The costs are for components, but excludes installation and tax.

A 4800 watt system could cost about $5,600.  As you can see, at the higher wattage the cost is approaching about $1 per watt. However, it is possible to get batteries for as low as $0.55 per watt.

Quick Comparison - AGM Limitations versus Lithium
It's useful to keep in mind that the list price of an additional 2400 watts of AGM batteries in a Roadtrek 210P is currently $871. The battery cost difference is why lithium is not currently standard. In recent years there have been some real price drops in lithium and today, 2400 watts of AGM batteries cost about $500-600 while similar lithium batteries begin at about $1,800.

However, AGM batteries are temperamental. They have longer charge times, can and do sulfate, weigh twice what lithium batteries do. AGM batteries perform longest with a 50% discharge (50% DoD, or Depth of Discharge). In other words, a lithium battery with an 80% DoD limit can provide 30% more power each and every day as compared to an AGM battery. Such a lithium battery is designed for at least 2000 cycles, which is about 7 times the life of an AGM battery. Achieving 5000 cycles would result in a system which could have a life measured in decades.

Of course, any RV manufacturer's pricing includes mounting and wiring systems as well as installation labor, etc. I am convinced I could install an entire system, including improved solar and MPTT charging system with at least 2400 watts (whr) of lithium power for a cost of about $3,000. If I want to get wild, I could go for 4800 watts at about $6,000.  The 2400 watt system would be almost a "drop in" solution. 3600 or more watts would require a closer look at the available battery space.

Other Battery Considerations
One more thing to consider is cycles. That's the number of times a battery can be charged and discharged. A Deep Cycle AGM battery, if discharged to not less than 60% the cycle life will be 300 plus cycles. (That's per reputable battery sources). An AGM battery might achieve 500 cycles. A lithium battery is good for 2000 to 3000 cycles at 80% DoD and ideal temperatures (see the notes). In other words, a lithium battery system is rated for a lifespan 6 to  10 times longer than that of an AGM battery system.  That is one of the reasons manufacturers are beginning to look seriously at replacing AGM battery systems with lithium battery systems.

What's the Limit?
Most costly component is the batteries. To get to 20,000 watts as Roadtrek is experimenting could require about $10,000-$12,000 in batteries (at wholesale). I would guess those batteries weigh about 500 lbs. However, to put this into perspective a Roadtrek 210P comes "stock" with two AGM batteries rated a total of 2400 watts. 4800 watts with AGM batteries weighs in at about 280 lbs.

What does 20,000 watts of AGM batteries weigh?
I'd guess that 20kW (kWh) of AGM batteries would weigh in at about 1,200 lbs plus the weight of the system to contain them. Similar capacity lithium batteries would weigh about 500 lbs. However, there are differing lithium battery technologies available, and that influences both volume taken by the batteries and weight. (See note 10).

Why would I do this? 
Well, I think I'll be replacing my AGM batteries next year, less than 36 months after vehicle purchase. Replacement with similar batteries will cost me about $600. In other words, the battery cost has been about $300 per year. Add to that the following possibilities achievable with an upgrade:

• zero maintenance with solar (I do have solar on the AGM batteries)
• no lead
• 10 year life (okay, let's assume 6 years at 75% real, available power).
• 80% depth of discharge
• A real 1920 watt-hour available rather than pretend 2400 which is at best 1200.
• I'd like to get more electrical power when off the grid than I do currently, and I'd like to achieve this without running the engine, or starting the generator. I'd also like to have more power available for cooking when off the grid and conserve propane. I have no intention of living on solar power.  The existing system is rated about 1.3kWh and I think I can double that with the lithium batteries. 
• No need to charge below freezing during vehicle storage. It's my understanding that lithium (LiFePO4) batteries should not be charged if they are below freezing. However, they can be stored for long periods under freezing conditions and can discharge okay in cold weather. (Note 11).

Notes:

1.  I have the advantage of being able to prototype and test such systems. I think a "drop-in" upgrade package for RVs would be useful.
2. I'm currently most interested in LiFePO4/LiFeMnPO4 battery technology. I want batteries which are safe.
3. Costs are determined by battery technology.
4. Battery prices are all over the map. Lowest cost is about $0.55 per watt (whr).
5. Battery life for AGM lead-acid and lithium (LiFePO4) batteries are determined under somewhat ideal conditions. Those conditions include ideal DoD as well as ideal ambient temperatures. Battery life is reduced under higher temperatures. What's ideal? Depending upon the battery, 74-77F is ideal.
6. In the real world some RVers are attempting to live off solar systems with lots of solar panels and large battery systems. This requires sunshine.  Unfortunately, many such sunny areas also get higher ambient temperatures and that's not good for batteries. Over in Tucson they talk about five annual seasons, of which one is named "fire." Elevated temperatures reduce battery life. So what's reasonable? I'm going to assume a 25% reduction in battery capacity within 5 years. However, for a  lithium (LiFePO4) battery that would be far superior to my AGM batteries.
7. A lot of what we know, and what we are doing, is based upon lead acid battery technology. For example, with AGM batteries it is preferred to keep them fully charged. So this approach was also applied to lithium batteries. However, there is now a concern that maintaining lithium batteries at full charge may actually reduce their usable life. In other words, there may be a trade-off and that has fueled some argument about what is the best way to maintain lithium batteries while achieving the longest possible life.
8. I am concerned about the above. A lot of what we currently know is based upon old lead-acid theory and requires years to validate in the "real world." When one is spending $thousands on batteries, that should be a concern. Roadtrek currently has a prototype with 20kW (kwhr?) of lithium batteries. Will they get it right?
9. Why do this? I'll post on that later, but I've provided a brief explanation in the text of this post.
10. You may wonder about that 20kW number. That's what a Roadtrek blog has stated a prototype lithium system has. I assume they meant a capacity of 20kWh (20 kilowatt hours). Not beyond the realm of possibility. I've seen a similar battery pack and it measures about 25 inches x 24 inches x 15 inches and weighs in at about 425 lbs.
11. It's my understanding that it's okay to discharge these batteries if the temperature is below freezing and they can be stored for long periods below freezing. However, they should not be charged if the temperature is below freezing. This will require some additional research on my part. 

Oops, I am so used to working in higher power systems I typed "kW" in several places when I should have typed "W." I have corrected this and now indicate "watts" where that is so. I also omitted the 120V charger for the lithium batteries on my list. It was included in the costs. It may not be clear from this post, but I could achieve an increase in available kW with the lithium batteries. My current 6V batteries are rated 220Ah under "ideal conditions."