Although charging a car battery while still connected or in situ is possible, various industry figures (like Halfords) suggest it's always a good idea to disconnect the battery before charging. In terms of invalidation cover, we also asked carmakers last summer whether trickle charging a battery would invalidate a warranty and most said no, as long as the handbook instructions were followed. However, some - like Honda - say the battery needs disconnecting or it will invalidate a warranty. Others will have that stipulated in the owner's manual. You can see the responses from manufacturers here: www.honestjohn.co.uk/coronavirus/coronavirus-will-.../