In my experience, a Mitchell 35mm camera fitted with a Jackson Woodburn motor is the best kit for timelapse.
The handbuilt registation and clawdown mechanism inside these vintage cameras is exceptionally steady, which may make a difference on a long shoot.
They are still used today for some SFX plate shots where steadiness is important.
And the Jackson Woodburn motors can be programmed with all manner of creative instructions like speed ramping or switching off at night.
There are many solar powered trickle chargers on the market for marine and leisure use, which could easily keep a 12volt camera battery topped up throughout your shoot period. I'm pretty sure a good camera hire company would have done something like this before and wouldn't mind their tech guys chatting to you about it. Good luck!
Ewan.
