I am asking specifically about automotive 12V lead acid batteries but I suppose the principles may be universal.
If I were to connect a fully charged 15V Li-ion battery to a discharged 12V lead acid battery (at around 11.5V), would the Li-ion battery charge the lead acid battery?
My theory is that since the potential at the battery terminals is about 14.7V when the car's alternator is running, attaching a 15V battery will have the same effect. Is this correct or will it result in some horrible acid flinging hydrogen explosion?