I think it's really continued use of quick-charging (e.g, DCFC) that can negatively impact the battery. Especially on the Volt, I don't think the L2 rates will cause much in the way of battery wear.

 

240V L2 is slightly more efficient than 120V L1, so 240V would actually be a bit better. But in the big picture, it doesn't matter either way.

 

Charge rate "harshness" on a pack is determined by percent of capacity (well, and temperature). So for gen2's 18.4 kWh capacity, a rate of 18.4 kW would be 1C (C=capacity). Anything below 1 is generally considered benign, you only start to see real effects above that (note that Tesla's superchargers are 90-120kW, giving them rates of about 1-1.5C depending on model). Even the latest optional 7.2 kW rate on 2019 Volts is only .4C, which is nothing to worry about. So the 3.6 kW standard rate or 1.4 kW 120V rate are 0.2C and 0.08C respectively, which are even less to worry about.

 

Exactly. As a rule of thumb any li-ion battery is ok to charge in one hour regardless of the capacity. Volt is far from that.

 

I think the charging rate and battery management is so conservative that there's no measurable effect of charging it on 240V vs 120V.

 

The answer is no.

 

Theoretically charging at a lower rate is better for the battery but as already noted even the latest 2019 Volt's 7.2kW charging rate is so far below 1C (18.4kW) that it hardly matters. A warm battery, up to an upper temperature limit controlled by the Volt's active battery thermal management system (TMS), is desirable for the most efficient charging. On more than one occasion I have observed my 2017 Gen 2 Volt charging using Level 2 in relatively warm conditions (air temperature 95F or higher) and the Volt's TMS will wait until charging has been completed before activating the AC to cool the battery. The AC and fan will then run for 10 - 15 minutes.

 

Charging ay higher voltage 240 vs 120 doesn't matter to the battery per se. Nor does charging at a higher amperage assuming the car's system is designed for it. The eTron charges at 20 miles per minute (figure out what the amperage is) and the Porsche and BMW cars coming out will be able to use the 450 Kw chargers so the paltry amount of electricity used by the Volt or Blot is nothing. The key is not the battery itself but the cooling system required to keep the electrics/battery cool enough.

 

It seems that using a 240V charger consistently would generate more battery heat when charging

The car circulates coolant through the battery to keep the temperature down and also heats up the battery when it gets cold, so the temperature conditions in the battery cells should be equivalent, no matter how one is charging up.

 

You're putting up to 59 kW into the battery pack every time you step on the brake.

I don't think the difference between 1.44 kW at 120V and 3.6 kW at 240V is significant. The pack is cooled to the same temperature regardless. Charging slows as the pack nears "full" in any case.

 

Don’t forget we are only using the 20-80% charge levels on the battery. The battery chemistry is very robust within this parameter.