Distributed battery charging

Hi all,

I have a solar panel setup on my shed, backed by some hefty lead-acid batteries. 12v system.

I have a requirement to get 12v in different garden buildings, greenhouses, poly tunnels, etc. I'd like to provide charging from a central point at the shed and distribute charging at ~3W to the end points so I won't need to run hefty cable as that would get quite expensive. I don't want a heavy load at the shed to pull power across from the small endpoint batteries - I could put in a diode but I assume the 0.7v drop would have an impact.

Are there any pre-designed solutions to address this requirement?

Thanks!