Renewable garden watering system - 12v battery system (solar recharged) to ensure there is 50l of water at 20ft twice a week

I have a load of water butt rainwater storage linked to my gutter downpipes for my garden water needs, but I can’t stand around waiting to fill watering cans from taps on butts, so occasionally (once a week?) decant (say) 80l from the water butts into plastic dustbins so I can then just dunk a bucket in the bin (takes seconds to fill) as needed and pour the water where it is needed.

However, I’d like to use a hose too, so would like a water butt (maybe 100L) high on an external wall to feed the hose by gravity…

The challenge is filling that elevated tank… As I’d only water maybe 50L twice a week, a weak slow pump to fill that butt is fine (solar powered, 100L a week, to (say) 20ft (6m)).

I’d appreciate any input/experience people can give before I start experimenting with this! I know mains powered water-butt pumps are available, but I am keen on an elevated ‘water tower’ for my hose… then I have options for how I get the tank filled.

Cheers