Is L1 8amp charging easier on the battery than 12amp?
The Bolt is designed so that the battery can charge with up to 50kW of power or more at the low end and around 10kW of power when it's nearly full.
120V/8A charging delivers less than 1kW of power, and 120V/12A delivers less than 1.5kW of power. Both of those are way, way less than the battery and its charging system were designed to handle, even for a full battery. So it's hard for me to believe that there would be
any noticeable difference between these as far as battery longevity goes.
I charge my battery using the OEM EVSE at 240V / 12A, which delivers less than 3kW of power, and IMHO the same comments apply.
An L2 EVSE running at the car's limit of 240V / 32A delivers less than 8kW of power, still less than the design point of the charging system. You need to use a DC Fast Charger before the charger's capability to deliver power exceeds what the car designers felt was acceptable, which for a battery that's nearly fully charged seems to be around 10kW. So L2 charging is getting closer to the battery's design limits when the battery is nearly full (but not when it's around 80% or less).
The big question is this: why you think that the car's designers chose that 10kW limit? Did they choose it because they were conservative and they felt that it was a safe level that didn't impact battery life significantly, or did they choose it because they wanted to push the battery technology as hard as they felt comfortable with in order to deliver faster charging times?
If you believe the former, you shouldn't have any issues with full L2 or DC Fast charging. If you're
very conservative and you want to do everything in your power to avoid stressing your battery even if it means longer charging times and potential inconvenience, then you might want to back off on those highest charging rates and avoid filling the battery completely unless you really need to.
Some folks with very high mileage and a history of using a lot of DC fast charging have reported pretty minimal battery degradation, which encourages us to believe that GM was pretty conservative with the design of its charging system.
Even so, because the Bolt has a lot of capacity and therefore a lot of range - more range than most of us need on a daily basis - limiting the maximum charge of the battery in normal use is a pretty common practice. It's easy to do, has minimal impact on your daily life, and is more likely to help the battery than hurt it. And it doesn't stop you from deciding to fully charge using a fast charger on those occasions when it makes your trip faster or more convenient.