hmm I like turtles as well but I'm not sure how practical it would be to wander around the infrastructure of the house where I will often go to add stuff. Though a persistent movement code will prevent them from causing problems if I encounter them, I tend to forget such things as their travel paths and might place something in their way when they are not there.
So in the current plan, when a battery is used up it will be summoned by the retriever and the filter will start sending out multiple batteries as it won't know its target can only take one. So they will be sent out and get stuck at the pipes till they are needed which will lag it like hell I assume. Reducing the timer frequency or placing a relay to return the excess batteries helps. But this is only with a small test system, I have no idea how will it be on a whole house. I might have to stick to turtles or abandon it all together.
(just to share here is the structure of the house: outer wall full block, air, inner wall cover, inside. It allows changing things without destroying and having to redesign the whole thing or looking ugly. outer block could be covers too for more space but I didn't want it to blow up completely if a creeper comes close, I will probably change it though.