I agree that comparing in watts is much easier and more realistic than talking amp hours, which is only relevant in the context of voltage.
To try and take this out a little further we need to do some more computing to make these numbers a more direct comparison. Specifically we need to account for 3 more variables: the Puekert coefficient, battery design life, and also the safe depth of discharge level. The problem is that all three of these values are a bit squishy, and/or up for debate as to what the correct value is.
Let's say you buy an Odyssey AGM battery. Under normal cycling they will tell you that the design life is about 10 years. Other AGM vendors might say 5 years. Some Lithium manufacturers will say 10 year design life. Flooded is more like 5 or so. How many years you actually get will of course be determined by how you use/care for them. It is quite likely that you would go through 2 sets of Flooded or inexpensive AGM's to one set of Lithiums. That would increase your cost per watt hour over a 10 year period by a factor of 2.
Additional concerns are that the estimated Puekert coefficients might be 1.0 for Lithium, 1.1 for AGM, and 1.3 for Flooded.
Estimated safe discharge levels might be 80% for Lithium, 60% for AGM, and 50% for Flooded.
So, at the higher rates of discharge that my boats typically operate at the cost per watt hour among the different types really start to converge. Flooded and AGM get more expensive, and Lithium choices seem more in line with the lead acid choices. Now we are looking at cost per "USABLE watt hour" numbers and can make smarter decisions on what would work for a particular application.
Capt. Todd
www.epowermarine.com
--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> wrote:
>
> So if we think in Wh, FLA cost about $0.10-$0.12/Wh, AGM cost between $0.20 and $0.25/Wh and Li is currently $0.45 to $0.50/Wh. You don't have to think about Ah or volts. Doesn't that simplify things?
>
> Since we discuss so many different voltages here, the common ones are 12V, 36V, 48V and 144V, talking in watts makes comparisons much easier for everyone involved. We already do for motors, it's not hard to do it for batteries too.
>
> Fair winds,
> Eric
> Marina del Rey, CA
>
> --- In electricboats@yahoogroups.com, Robert Lemke <robert-lemke@> wrote:
> >
> > Price domestically is running $1.30 per a/hr per 3.2 volt cell. So, 48 volts @ 200 a/hr should be 1.30 X 200 X 16 (for 48 volts) = $4160.00. Sound about right?
> > Bob aka "deckofficer"
> >
>
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