How environmentally friendly are electrobikes?

Obviously we read any bicycle catalogue that comes into the house. I've noticed over the years that there is a tendency for advertisers to claim that their e-bikes are CO2 free. However, unless an owner has a wind, hydro or solar power unit to charge his or her e-bike some of the power used to charge the battery will have been generated by fossil fuel fired stations, except if you live in France where the majority of electricity is generated by nuclear stations.
As well, the extraction and purification processes of the components of the lithium ion batteries normally used in e-bikes need power, i.e. generate CO2. After several hundred charge and discharge cycles the battery's capacity is much reduced. The battery needs to be replaced. Traditionally at least in my experience old mobile phones are popped in a drawer and forgotten about. Whether this happens with bike or even car batteries, probably not, but at the moment recycling rates are between 4 and 5%. Recovering metals from lithium-ion batteries has a 90% smaller ecological footprint than primary mining.
There is a lot of room for improvement in bike battery recycling, but on the other hand a car not only emits CO2, but also other combustion products, so cyclists even e-cyclists are helping air quality by  emitting less CO2 and filtering combustion products through their lungs. In addition CO2 output is directly related to the weight being moved. A VW Golf weighs about 1500kg (1.5ton). A fat cyclist on an e-bike has a total weight of 150kg, i.e. 10% of a motorist in a medium sized car, so the CO2 output will be much smaller.
The answer to the question is "yes e-bikes are environmentally friendly, but better battery life and recycling will make them even more so".

Why should I ride a bike regularly and leave the car at home?

There are all sorts of reasons:

• Financial Reasons: Bike riding is cheaper. An expensive bike costs five thousand Euros. You can purchase a new reasonable bike for between five hundred and a thousand Euros. A decent two or three year old second hand car will cost you a lot more. 
• Cycling is as quick: Bike riding is as quick as a car over shorter distances, if not quicker, if you take the time to find a parking space for your four wheeled vehicle in to consideration.
• Health Reasons: Bike riding is healthier. 
• Environmental Reasons: Bike riding is better for air quality because you are cleaning the air rather than filling it full of carbon dioxide, carbon monoxide, nitric and nitrous oxides, lung clogging unburnt tar particles, etc. etc. However you should then try to get out of town now and again to give your respiratory passages a chance to recover.
• Patriotic Economic Reasons: Motor cars and bikes need oil to power them. Although Britain does still have North Sea oil, it has imported more oil than it has exported since 2003, so if the country can reduce its appetite for oil, it will spend less money abroad and so improve the balance of payments. Cyclists don't use much oil, so every kilometre you can ride on a bike or walk instead of sitting in a car is good for the nation.