[meanderingthemaze]

So, by now, I think many of you know I've been perusing the boards for awhile now. I've heard a lot of fanatics on either side of the argument. But to me, after crunching real numbers, and unfortunately only having access to a lot of anecdotal case studies, the case is not clear. It's quite grey actually when it comes to the most important aspect of the DIYer's decision making process: ROI.

I know this has been discussed to death, but I am hoping that I can task the users of this forum to consolidate what they understand into USEABLE and ACTIONABLE information for other DIYers on the board since this is the perennial question in this subforum: Lead or Lithium?

I am hoping that this discussion will not be about ego or being right and wrong but rather an unbiased, fact-based presentation of information so that we can empower other converters to make informed decisions and quit posting the same darn question over and over. That means that you should provide facts and sources to support your claims and state your assumptions!

Here's a simple "Battery Calculator" I did for myself to make it easier to investigate a variety of pack configurations quickly. If someone has something better, please post. The $ figures in there are estimates, but based on real world market figures and the sources of the information are given.
https://docs.google.com/spreadsheet/...UtLdEstQ040SlE
Or this may work better:
https://docs.google.com/spreadsheet/...SlE&output=xls

Indisputable things Lithium has going for it:

1. Energy density - can pack more electrons into a lighter box leading to better potential range.
2. Power density - can release and absorb more electrons quicker leading to better acceleration/charging characteristics.
3. Lower Peukert constant - has lower internal resistive losses during discharge/recharge, which leads to better effective energy density and thus better potential range.
4. Useable life - higher cycle life and potential age
5. Labor - over the life of the vehicle, there would be less battery swaps and therefore less labor hours. also no maintenance.

Indisputable things Lead has going for it:

1. Initial cost - significantly cheaper upfront costs.
2. Simplicity - with no need for a BMS, the overall energy storage system is simpler, ie: less complex.

The grey area, but the most important point to most people:

1. ROI - Based on effective kWh, doing an apples to apples comparison. I'm seeing a 5-6 fold cost diff b/t the two. This means Lithiums would have to last for 10-12 years to break even, at two years per Lead pack, being conservative.

I'd like to see more thorough fact based analyses about ROI. Most of the ones I've seen before rely on some very ambitious and possibly dubious premises. Speculation can lead to even more grey area, so let's deal with what we really know right now.

Unless there has been recent information I'm not aware of, claims of the longevity of Lithium need an asterisk next to them because there is no realistic way to simulate the aging process. Cycling batteries gives some information, but until we see some real world examples, like we have with Lead, of Lithium packs lasting 15 years, then please accept and state your analysis is based on an unproven assumption of lifespan.

I look forward to a constructive discussion. Thanks

[Ziggythewiz]

It feeds into ROI, but cycle life should be in the list for pros of lithium.

Also, I'm not sure where you get that lithium costs 5-6x lead. Everything I've seen is lithium around 3x the cost of cheaper lead options, and only double or less that of the higher end lead options.

More anecdotal evidence for you: When my lead began to die it was one at a time. I wasn't going to throw away the old and replace with new, especially since they were under warranty, full then prorated. It took about 8 months to transition from one pack to the next, which saved over $700 vs dumping one pack and switching for the next, but is cost countless hours in circuit reconfigs to keep things running over that window.

[dladd]

Originally Posted by meanderingthemaze

So, by now, I think many of you know I've been perusing the boards for awhile now. I've heard a lot of fanatics on either side of the argument. But to me, after crunching real numbers, and unfortunately only having access to a lot of anecdotal case studies, the case is not clear. It's quite grey actually when it comes to the most important aspect of the DIYer's decision making process: ROI.

I would question your premise. I do not think ROI is the most important aspect of the DIYer's decision making process. I'm not sure it was even in my top 5! Hell, from an ROI standpoint, I'd be ahead driving around in a 15 year old 30mpg Saturn than spending 15k to convert it to battery power...

and fwiw, I have not heard from these lead acid 'fanatics' at all. In fact, it seems fairly universal. Even those who have lead would prefer lithium. No one with lithium wishes they had stuck with lead. Well, maybe I shouldn't say 'no one', I'm sure there's someone out there that will say that. Certainly the upfront cost is high, and prohibitive for some. BUT, if you can swing it, Lithium is clearly better. In the short, and in the long run.

lithium is most likely better on ROI, but as you say, how can that be guaranteed since lithiums haven't really been used for more than a few years yet? It does seem clear though, an EV in daily use of any decent range will ruin it's lead pack in 2 years. I've read about that happening time and time again. Some may claim 5 years on lead, but that's going to be occasional use, short trips, and intensive babysitting of the batteries.

I'm not sure where you are seeing a 5-6x increased cost for Lithium, i think it's more like 3-4x at most. Making the crossover more like 6-8 years. Initial data shows that lithium cells will probably last that long, but it's no guarantee. However, in the mean time you'll have better range, better performance, less weight, and higher efficiency. Plus, you won't have the hassle of swapping out battery packs every 2 years.

[meanderingthemaze]

Originally Posted by dladd

I would question your premise. I do not think ROI is the most important aspect of the DIYer's decision making process. I'm not sure it was even in my top 5! Hell, from an ROI standpoint, I'd be ahead driving around in a 15 year old 30mpg Saturn than spending 15k to convert it to battery power...

and fwiw, I have not heard from these lead acid 'fanatics' at all. In fact, it seems fairly universal. Even those who have lead would prefer lithium. No one with lithium wishes they had stuck with lead. Well, maybe I shouldn't say 'no one', I'm sure there's someone out there that will say that. Certainly the upfront cost is high, and prohibitive for some. BUT, if you can swing it, Lithium is clearly better. In the short, and in the long run.

lithium is most likely better on ROI, but as you say, how can that be guaranteed since lithiums haven't really been used for more than a few years yet? It does seem clear though, an EV in daily use of any decent range will ruin it's lead pack in 2 years. I've read about that happening time and time again. Some may claim 5 years on lead, but that's going to be occasional use, short trips, and intensive babysitting of the batteries.

I'm not sure where you are seeing a 5-6x increased cost for Lithium, i think it's more like 3-4x at most. Making the crossover more like 6-8 years. Initial data shows that lithium cells will probably last that long, but it's no guarantee. However, in the mean time you'll have better range, better performance, less weight, and higher efficiency. Plus, you won't have the hassle of swapping out battery packs every 2 years.

You are right to question my premise as I am using anecdotal evidence from what I've seen on the boards. Most people seem to be most concerned about finances, even though there is a subset of people, like racing enthusiasts or wealthier individuals who can afford to play with their money more. Even if this thread is only for those that are concerned with ROI, then I think it's worthwhile to lay out the cards on the table for analysis.

I've updated the above Lithium pros list to include less labor, since you bring up a good point about the work involved in switching packs.

As to the 5-6x cost, check out the spreadsheet I've linked to to see the figures. I'm comparing kWh. However, I should be comparing effective kWh, so maybe it is closer to 4x. I'll double check that now.

[subcooledheatpump]

This goes along with the BMS thing, but what about safety issues? Lithium, as I understand because of it's high energy density, can be quite explosive if the cells overheat or are exposed to overvoltage/overcurrent. Lead batteries are much more tolerant to overvoltages. No BMS to worry about for charging, but also for those (like myself) with Regenerative Braking, it means you won't have to stress when the voltage climbs up during Regenerative Braking. Just my thoughts

[Ziggythewiz]

Lead I pay about $310 per useful kwh, lithium would be around $558.

Part of the expense with lithium is that if you're going to spend that much anyway, why not spend some more and get 50 miles instead of 30. I could get the range I need out of 60 AH cells, but I'd rather save up and get 100s.

[PTCruisin]

Here is another "data point" regarding ROI:

I spent $5600 for a 12kWh LiFePO4 pack nearly two years ago. I drive an average of 20 miles/day, 7days/week, 50 weeks/year. Annual driving = 7000 miles.

The cost to charge the pack after the 20 mile commute is approx 50 cents - based on 8kWh from the wall plug @ 6.5 cents/kWh.

When the vehicle was ICE-powered, I would use 1 gallon of gas for the same commute @ $3.75/gallon on average.

Annual fuel costs = $1300
Annual electricity costs = $175
Annual savings = $1125

$5600/$1125 = 5 years to pay off batteries with cost savings.

So ROI is at 5 years. Since I use about 50 to 60 % of the capacity, I expect to get around 10 years of service out of the pack.

I know this is not comparing Li to Pb but I expect you would have to replace the Pb after 2 or 3 years anyway.

[somanywelps]

Originally Posted by PTCruisin

$5600/$1125 = 5 years to pay off batteries with cost savings.

And then you have very low (no?) maintenance and HOV access and not having to stop at gas stations.

[meanderingthemaze]

Originally Posted by Ziggythewiz

Lead I pay about $310 per useful kwh, lithium would be around $558.

Part of the expense with lithium is that if you're going to spend that much anyway, why not spend some more and get 50 miles instead of 30. I could get the range I need out of 60 AH cells, but I'd rather save up and get 100s.

So, this is an area I'd like clarified with calculations. I think it's very difficult to gauge useful kWh in a pack given the number of variables involved. However, is there a rule of thumb for adjusting the advertised AH rating given by manufacturer to the effective useable kWh that you'll see in your conversion? If so, please share. I'm curious to see how you are calculating that. Someone else in another thread suggested at 1C discharge that Lead would decrease to 65% of the advertised 20 hour rate.

Also, your cost sounds ridiculously expensive for Lead. Are you using AGMs? I think we should talk about wet batteries as they are the most widely used and the best cost advantage. I'm not sure how AGMs would be used.

If you check the above calculator link, it shows that a 6V 232AH lead battery costs $90. That's 90/6*232 = ~$65/kWh. However, if we say they're 65% efficient, that raises the number to ~$100/kWh. If Lithium is @ $558/kWh, you can see how I'm getting the 5-6x difference.

You could argue that you need less Lithium than you would Lead because the vehicle is lighter, but by how much? Factor that in and again, I don't see how it could be better than 4x difference.

In my opinion, the difference between Lead and Lithium costs need to be closer to a 1:3 to make it feel like a good investment, or better yet, 1:2...IMO.

[evnz]

ROI mean what?