
#1
Dec1112, 07:42 AM

P: 59

Hello,
I have seen graphs of Battery's DoD (depth of discharge) vs Life Cycles. But at the same time, "life cycle" is defined as the no. of COMPLETE chargedischarge cycles that a battery can perform before its nominal capacity falls below 80% of its initial rated capacity. Here's the contradiction: From the definition, the term "life cycle" should only be valid for a DoD of 100% (or maybe 80%, whatever is the max. possible value). How can the battery's life be rated in terms of life cycle? In those graphs, does "life cycle" simply mean discharging to a specified amount (DoD) and then charging rather than COMPLETELY dscharging and charging the battery? 



#2
Dec1412, 03:53 AM

P: 2

Yes, you discerned it correctly, the graph measures the life of a battery [defined as having worn to the point of 50% of nameplate capacity] vs the DoD [Depth of Discharge]
However, out in the real world, with scooter and power wheelchair batteries I see lifes much shorter than I would expect based on these graphs. I see commonly AGM batteries lasting 23 years. At one cycle per day, that is ~600900 cycles. At a mere 10% DoD AGM batteries are expect to last {ON Average} over 2000 and Gel batters over 6000 over 10 years! This does not happen out in the real installations. Open Questions to me: 1. Why not? Is it something to do with the moving / shaking causing the premature battery failures. Is perhaps the quality / size of charger? Maybe the load current is higher in the scooters? Do not know. 2. The graphs of DoD all start at approximately 10% what happens at 5%? 



#3
Dec1712, 06:13 PM

P: 1

There's an interesting article here that might illuminate what's going on. Apparently, leadacid batteries, regardless of the type, have a fairly narrow chargedischarge window, and going outside it stresses them. That's why car makers are so interested in Liion, which has its own set of problems, of course.



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