3 ms·

When speaking of battery cycles and lifetime, people almost always mean "full cycle equivalent". So when you say "I only go 80%->20%" then that would be conside

by coryrc 4y ago

When speaking of battery cycles and lifetime, people almost always mean "full cycle equivalent". So when you say "I only go 80%->20%" then that would be considered 0.6 cycles counted against the lifetime.

manmal 4y ago
I don't, LFP batteries are quite resilient. 80% -> 20% is a usability nightmare nobody with a $50k vehicle should accept. My Ioniq (first gen) doesn't even have an LFP battery and is optimized for 100% -> 13%, maybe even 100% -> 10% (turtle mode starts at 5%). Still at 100% SOH after three years. Way more important for battery life is the charging rate (again, LFP are more resilient there too). Which wouldn't be an issue for grid use.
- coryrc 4y ago
  I think you do. If you drove 10 miles and recharged, you wouldn't consider that a "cycle". You could do that 100k times (probably more), but no one would say the battery cycle life is 100k.
  - manmal 4y ago
    I mean I didn’t count in 0.6 cycles per discharge. My battery does 0.9-0.95 cycles usually.
throwaway894345 4y ago
Is that how it works? Can I just charge every night, even if I've only driven a few miles, with no more wear on my battery than if I did full cycle charges? My vague impression is "no", but I really have no idea.
- coryrc 4y ago
  It is, with lithium, basically no different to go from 80%->20%->80% once or from 80%->75%->80% twelve times. The only complicating issue is calendar life of the battery when it is above 80%. Over time a battery loses capacity just because it exists, which I'm calling calendar life. The closer your battery is to 100% the calendar life decreases at a roughly quadratic curve (a battery at 80% has about 1/8 the calendar life loss of one at 100%). AKA you lose 8x more capacity per year at 100% than 80%. Temperature has a similar effect above room temperature or so. So if your frequent charges keep the battery above 80%, that would reduce calendar life (increase capacity loss per year) on its own. LFP has far greater calendar life than lipo, but also cycle life too, so I think it's just as important to keep your EV at 80% or below, whenever convenient, regardless of chemistry, unless your usage will cause cycle life to end the battery usefulness before calendar life is significant; i.e. multiple full cycles per day. But also at multiple full cycles per day you probably won't spend much time above 80% even when charging to 100%. Ah, to summarize, I'll repeat my simple advice: I think it's important to keep your EV at 80% or below, whenever convenient.

by coryrc 4y ago

manmal 4y ago

I don't, LFP batteries are quite resilient. 80% -> 20% is a usability nightmare nobody with a $50k vehicle should accept. My Ioniq (first gen) doesn't even have an LFP battery and is optimized for 100% -> 13%, maybe even 100% -> 10% (turtle mode starts at 5%). Still at 100% SOH after three years. Way more important for battery life is the charging rate (again, LFP are more resilient there too). Which wouldn't be an issue for grid use.

coryrc 4y ago
I think you do. If you drove 10 miles and recharged, you wouldn't consider that a "cycle". You could do that 100k times (probably more), but no one would say the battery cycle life is 100k.
- manmal 4y ago
  I mean I didn’t count in 0.6 cycles per discharge. My battery does 0.9-0.95 cycles usually.

throwaway894345 4y ago

Is that how it works? Can I just charge every night, even if I've only driven a few miles, with no more wear on my battery than if I did full cycle charges? My vague impression is "no", but I really have no idea.

coryrc 4y ago
It is, with lithium, basically no different to go from 80%->20%->80% once or from 80%->75%->80% twelve times. The only complicating issue is calendar life of the battery when it is above 80%. Over time a battery loses capacity just because it exists, which I'm calling calendar life. The closer your battery is to 100% the calendar life decreases at a roughly quadratic curve (a battery at 80% has about 1/8 the calendar life loss of one at 100%). AKA you lose 8x more capacity per year at 100% than 80%. Temperature has a similar effect above room temperature or so. So if your frequent charges keep the battery above 80%, that would reduce calendar life (increase capacity loss per year) on its own. LFP has far greater calendar life than lipo, but also cycle life too, so I think it's just as important to keep your EV at 80% or below, whenever convenient, regardless of chemistry, unless your usage will cause cycle life to end the battery usefulness before calendar life is significant; i.e. multiple full cycles per day. But also at multiple full cycles per day you probably won't spend much time above 80% even when charging to 100%. Ah, to summarize, I'll repeat my simple advice: I think it's important to keep your EV at 80% or below, whenever convenient.