The only necessary CO2 release from batteries is based on the current state of our global economy. Reduction in the amount fossil fuels used in the grid and mining equipment directly reduces the use of fossil fuels manufacturing batteries and solar panels all the way down to zero.

As part of being massively more expensive, Nuclear actually involves significantly more indirect fossil fuel usage due to those costs. For example all a nuclear power plants requires onsite fossil fuel generators which need to be run regularly: http://aa-powersystems.com/wp-content/uploads/3061871_OE_Bro... Yet those generators are left off of assessments of CO2 releases associated with nuclear power plants. Similarly the centrifuges reacquired to manufacture nuclear fuel require vast amounts of electricity to manufacture and run. The nameplate generation from Nuclear further ignores those ongoing energy costs.