Part 4
Previously ….
“Generally, people install Lead Acid Batteries in their Recreational Vehicles and Boats to run the everyday Habitation/House services. But there is increased interest in Lithium Batteries (and particularly the LiFePO4 style of Lithium) as they offer various benefits and advantages over Lead – however up-front cost is definitely not one!
But what about the idea of using both at the same time, maybe taking advantage of both Lead and Lithium at the same time? Wouldn’t that be cool if it were possible? Well, maybe it is ….”
The previous pages discussed the theory and the practice behind having Lithium and Lead running. And then we went into some details regarding charging considerations.
In this 4th and final Part, we conclude the discussion.
Please Note: The content here is provided as general advice and information and is not specific to YOU or YOUR vehicle.
It should be used at your risk, is not warranted or guaranteed in any way and we are not liable for any losses or damage that might occur.
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Conclusions
This installation is still pretty young [installed in May 2021], but I think I can make some conclusions on the Hybrid Setup.
As the mathematics predicts, the Lithium Part of the Hybrid Battery has priority. What I mean by that is that when any general loads are drawn, it is the Lithium Battery that provides the energy almost exclusively until it gets to a pretty low State of Charge. It should be noted that when there is a large load which results in a significant voltage drop, this does result in the Lead Bank coming into play to assist, which is of benefit to the overall bank as it reduces significantly the situation where a current draw might exceed the Rated current limit of the Lithium Battery.
The result of this is that cycles are taken out of the Lithium Battery, which typically copes a lot better in that respect, than the Lead Acid Battery, prolonging the life of the Lead Acid. It shortens the potential life of the Lithium Battery, but as the life of those, based on charge cycle count, can theoretically be in decades, does that matter? Chances are that in say 10 years time, the replacement for a LiFePO4 battery will be more efficient, small and cheaper and you may swap over the batteries anyway in the same way you might replace your car for a new one despite it still being perfectly serviceable still.
The other key result of this is recharging is very much Lithium-orientated, which means a faster and more efficient recharge compared to Lead Acid.
Even when the amount of power taken means you have used the Lead Acid a lot as well as the Lithium, it is the Lithium Battery that gets the greater share of the charge current, which means that it is ready to provide power again quicker. So the charging system on a Hybrid setup becomes more efficient compared to a Lead Acid configuration.
Battery Costs
Cost comparisons are a bit tricky.
Battery Life is generally specified in terms of Recharge Cycles and how many Recharge Cycles it takes for the maximum capacity to have dropped to 70% of its original capacity. How many Recharge Cycles until that happens depends on a number of factors and a key factor is how deep a discharge a battery gets before it is recharged. Yes, you can take a Lithium battery down to 100% DoD (so empty), but you might halve the number of cycles it is capable of compared to maybe a 80% DoD. And if you only go down to 60% DoD, you get even more Cycles from the battery. The same principle is true of Lead Acid, but typically the DoD – Depth of Discharge – permitted for Lead Acid is a lot less to achieve a reasonable cycle count, and for most regular Lead Acid batteries, the count is already a lot lower than Lithium. Note that there are some Lead Acid Batteries – Lead Carbon technology – that are capable of a much lower DoD and have a increased Cycle Count as well.
What does all this mean?
When you look at the overall lifetime cost, a Lithium Battery Bank can work out cheaper per AmpHour taken but will have a much greater up front cost. Depending on how you use the batteries, the payback time compared to Lead Acid (i.e. the point where investing in Lithium has saved you money) will likely be many, many, years in all likelihood.
A pure Lead Acid battery setup will be the cheapest initial way to get a good level of capacity in a Leisure Vehicle or Boat, but you would likely be replacing the battery bank 2 or 3 times before you replace a Lithium Battery. At which point your overall cost is similar to what you may have paid for Lithium initially, plus you won’t have benefited from the undoubted advantage of Lithium’s more efficient recharging characteristics at any time.
Adding a Lithium Battery to a bigger Lead Acid Bank to create a Hybrid Bank means you are able to have a fairly large Battery Bank at a much lower initial investment compared to that same capacity in Lithium. Additionally, you also get the benefit of Lithium for the initial power delivery and the speed/efficiency of Recharge. This results in the Lead Acid part not being taken to the same level of DoD as in the pure Lead Acid Bank, and so improves its projected service life and saving overall costs on the Lead side.
The Lithium Batteries in a Hybrid Bank would likely be taken lower than a pure Lithium Bank, reducing its Service life in terms of cycle count, however those cycles are so high according to the manufacturers projections, the impact of that could be you need to replace the battery in 10 years instead of 20 years. Is that really a concern with the way Lithium Batteries are projected to improve further and at a lower cost (note my earlier car analogy)?
Hybrid vs Lithium vs Lead Acid
If your need is just 100 to 200Ah, then sticking to a single technology is likely the best option for simplicity, but when you go to 300Ah or more, than a Hybrid setup becomes interesting and as you go bigger, the system & cost advantages become more and more apparent and attractive.
I plan to do some cost-benefit analysis on this in the future and hopefully even have a calculator which can tell you a potentially optimum setup for cost vs capacity, but this will be based purely on the maths as opposed to this report which is based on real data.
The Final Word
I hope this has been of interest and if you have got as far as reading this, well done! If there is any thing further you would like to know, or any points you would like to discuss or you disagree with, use the Contact form to leave a message
If you are a supplier of Batteries or Chargers and would like to know more about the methodology I employed, or even have your products tested/compared, please contact me using the form as above.
If you are interested in the VSDR-200 Charge Control unit, there will be a product page in the shop, and in the meantime you can contact us for further info directly via the Contact Us Page
Thanks for reading,
David.