Yes if your goal is to maximise battery life. But there are other things to consider.
Let's say your daily commute is 20 miles. A 40% DOD pack gives you the most total range, so if we want a 40% DOD pack we need a pack with a 100% DOD range of 50 miles. If you chose a pack that requires an 80% DOD to go 20 miles then it's roughly 1/2 the size AND WEIGHT of the 40% pack. This means that it also costs only about 1/2 as much. On the down side the 80% pack will probably only last 11,200 miles vs. the 28,00 miles of the 40% pack. Of course if the 80% pack costs 1/2 as much then for the same price we can buy two 80% packs and get 22,400 miles. This is a little bit easier on the wallet (we spread the costs out over several years), but still gives us fewer miles per dollar. But there is the weight issue. With the same controller and motor the 80% pack will accelerate faster, have better handling and overall better performance. Plus you might have more available payload capacity for carrying more stuff (or at least stay under your max allowable weight). Of course you can always go with a bigger controller for the heavier pack, this just costs more money. Then there is the issue of current. The posted charts were undoubtably done at a constant current draw, probably either at the 20 hr rate or (if we are lucky) at the 75 A rate. But even 75A is below what the typical EV averages and peak currents can be up to 8 times this or more. I think that these peak currents kill the batteries long before they get to the number of cycles posted. In fact since the 40%A pack lasts longer it will see many MORE of these peak currents and it's even possible that the overall life of the 40% pack might be equal to that of two 80% packs. Now we get to the real BIG down side of the 80% pack, range. Sure it can handle our average commute. But what about those days when we want to make a side trip to the mall or forget something and need to go back home for it. At least early on the 40% pack can do our 20 mile commute twice without charging. I think, for most people, this reason rather than bang-for-buck is why they shoot for 40% DOD. Of coure the reality of home conversions is that you figure out how much weight you can carry, how much space you have available, how much voltage your controller can handle, and you stuff in as many batteries as you can get that meet these requirements. Afterwards you live with the range you end up with. P.S. Personally I shoot for 40% when designing an EV at least that's what I'm shooting for on my next one. > Martin Jackson wrote: > >> Nawaz Qureshi of USB made a graph of # cycles vs. % DoD that I got >> somewhere. I don't think it's on their web site. I picked off the >> numbers: [chart deleted] > > > So I gather the take-home message is that this is very much a > battery-specific exercise. The various numbers thrown around briefly > in this thread seem to imply that staying under 50% DoD for most > battery types is the safe way to maximize energy return, but that this > has little or nothing to do with the company-asserted "cycle life". > So unless I'm familiar with the actual data from a particular battery > type, I should take lifetime mileage estimates with a grain of salt, > and should try to stay under half the rated maximum range between > rechargings if my goal is to maximize battery life. > > Is that a fair summary? >
