Sagging Blues: why EVs are not for everyone right now

November 22, 2007 by Rob.

Sagging sucks! Sagging is the term for the voltage drop batteries experience while delivering current. Fresh batteries have minimal sag while dead batteries may look like they have charge but will sag way way down if you use them. That makes it hard to really know how much power you’ve got available.

When my batteries are low they sag way down (50% of full voltage) and the RAVolt creeps slower and slower. The more you stress them, the more they sag. Around town it’s fine, but it’s no fun to be climbing hills on MoPac or 360 with low batteries. Tired batteries like a little rest and pulling high amps on a hill is hard work!

I saw a thread moaning about this on the EVDL and I believe that it’s the #1 reason why EVs are not ready for the mass market. It’s a downer that the RAVolt’s performance degrades as I drive it. This not about limiting total distance, it’s about the last 25% of my drive being slower than the first 75%.

While I live with it daily, I also recognize that its a hurdle for EVs to overcome. Anyone want to buy me some Lithium batteries?

NOTE: I want to clarify that not all batteries have the same discharge characteristic. Before EVeryone flames me - I’m speaking from my experience with floodies (flooded lead-acid). Please chime in if you have different experience with other chemistries!

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