for some reason it is more difficult to slow charge many aircarft's batteries than it is to supply ground power for a "jump" start, because hte battery does not charge through the external power plug, but has to be accessed directly.
Yes; it's usually awkward to get to the battery.
A lot of people in the USA installed a battery charging connector. It's just a connector which comes out somewhere, and which connects directly to the battery, via a fuse located close to the battery.
There are protracted arguments in the usual places as to whether the connector requires an STC 
There are also specialist "aviation" battery chargers which run special pulsed charging profiles, to remove sulphate from the plates, etc. One quote I had was about $400 including some outrageous shipping cost. This is a popular type: E24041-AA-S2
A lot of people in the USA installed a battery charging connector. It's just a connector which comes out somewhere, and which connects directly to the battery, via a fuse located close to the battery.
Yup, that's exactly what I have done. Whenever the airplane is in the hangar, a CTEK charger is attached. They do exactly what your $400 charger is supposed to do, probably even better. Everybody I know in the oldtimer car scene got one of them for each car.
I’ve just come across this
It contains the fuse which is required to be close to the battery.
It still isn’t suitable for installation in the airframe skin (that would need a waterproof connector) so you need to open a hatch or something to plug the charger in.
Thanks Peter, that’s useful! On almost all my vehicles I have installed a charger harness with the SAE connector, but have never installed one on the plane because its a visually obvious non-aeronautical part. I think I’ll get one of these from Sporty’s. With the charger harness I wouldn’t have to pull the battery box lid. My plane has an access door for battery box access, so no problem there.
Rex Box uses the same connectors ob their battery boxes.
If this was me, I would try to fit an external connector.
There are milspec connectors which have a watertight screw-on cap. In fact there probably are connectors which are totally waterproof (immersible) when simply disconnected, as e.g. used on military radios.
Then one could charge the plane without it being open to anyone to nick stuff out of it.
This is another solution
In bright sunlight this will fully charge a 15Ah battery in 15hrs. So basically it will take a day to put enough in to start the engine.
I used to carry this when travelling, rolled up in a tube about 10cm x 40cm.
till it gets nicked.
Peter
Some time ago there was a thread about battery charging via (if I remember correctly) a rather small device which stayed connected to the batter. I have done a search but cannot find it. Can you help please?
Thanks
The Solar panels are great and would be particularly good for a non-generator antique with a battery to power the radio.
My battery access door doesn’t allow access to the cabin, but on the other hand I’ve never locked the cabin anyway. Usually for short stops I leave the mag switch key sitting on the top of the instrument panel.
