Fossa wrote:Lithium battery is an absolute must for an electric vehicle.
Well, for an electric skateboard, maybe so. But lead-acids have their place in electric cars and such.
There are three major types of lead-acid battery: gel cells, AGM, and flooded. The first two are sealed, the third is not. The gel cells are the type that's finicky about charging and has all the other associated problems: they're only really useful for things like motorcycle starting batteries or something comparable that doesn't require fast charging or deep discharge but does need to be portable and sealed. AGMs are expensive (well, expensive for lead-acids--Li-ions are in a whole world of their own when it comes to cost), but they're not quite so finicky. The reason for the trouble with gel cells is that the gelled electrolyte can't move around much, so if overcharging makes bubbles of hydrogen, or if quick discharging "uses up" the electrolyte in contact with the cell plates, it takes a long time to move around and expose the plates to fresh electrolyte. AGM batteries use liquid electrolyte in fiberglass, and they don't do this as much. Gross overcharging can still damage the cell, though, because they are sealed, but that's true of just about every battery chemistry.
Flooded batteries obviously wouldn't work for an electric skateboard (because they would dump acid everywhere if you flipped the board upside-down!), but they can be built for very long life, and are difficult to damage by overcharging. Even severe overcharging can usually be remedied by refilling the electrolyte with distilled water. They're great for electric cars, though, even despite their size and weight, because they're so cheap and readily available in high-current, high-power deep cycle configurations that are designed for traction use (electric forklifts, golf carts, and so on).
All lead-acid batteries suffer from sulfation, which is easy to prevent--keep the batteries fully charged whenever they're not being used. Flooded batteries are particularly easy to do this with--since overcharging doesn't hurt anything, it's possible to periodically run a leveling charge until every cell is fully charged. With many other chemistries, failing cells have to either be ignored, or be pulled out and charged separately or replaced--and usually that means replacing the good cells attached to them, if the cell is part of a battery.
Now, before I get too far off topic: It doesn't say specifically, but I'd bet that skateboard above uses gel cells. AGMs will still not have the performance of Li-ions, but they're an alternative to consider. Another intermediate, if such a thing is commonly available for electric skateboards, would be NiMH batteries. These are cheaper than Li-ions and have better energy density than lead-acids, and are generally reasonably tolerant of weird charging schedules.
I don't know how well my figures will apply for an electric skateboard, because I was looking at bulk prices, but when I priced out batteries for the electric car I'm building, here's what I came up with:
A full pack (in the neighborhood of 120V and 220 Ah) of flooded lead-acids will cost about $2000 and last for approx. 1000 (full) cycles. Weight would be about 1500 lbs. (This is what I'm going with, by the way. I can get the exact cost and weight if anyone's interested.)
A full pack of AGM batteries will cost about $3500 and last about 1000 cycles. Weight would be about 1200 lbs.
A full pack of LiFePO4
batteries would cost about $11,000 and last for approx. 5000 cycles. Weight would be about 600 lbs.
I never priced Li-ions seriously, but the price would be above $20,000 for a pack (maybe well above, it's hard to find bulk sources), and lifetime would probably be about 1500-2000 cycles. They would weigh about 400 lbs.
Note that LiFePO4
batteries are surprisingly cost-competitive over their lifetime. I doubt you can get a commercial electric skateboard that comes with them--they're relatively new technology (discovered in 1996, only commercialized in the last few years), but if you wanted to DIY a really good battery pack, this is what you'd use. Of course, I'd love to have an electric-car-sized set of them, but I don't have the money for that kind of investment right now.
. . . Okay, this is probably more about batteries than anybody ever wanted to know. Hopefully there's something useful in there.