I want to trickle charge the 12v. battery in my Mk. 4 Jazz and it's not possible to use a 13 amp plug as I have to park in the road. I don't want to use a solar panel device as I found them to be somewhat ineffective, so I wonder if there's a charger that is self contained, that will sit under the bonnet, and has a built-in rechargeable battery itself, rather like one of those portable self-contained tyre inflators.
I haven't seen one so maybe they don't exist, but interesting if they did.