The Crooked Box Off-Grid Auxiliary Battery System

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Crooked Finger Designs has a long history of designing and installing off-grid electrical systems for rigs. We do large systems, and small systems, but our specialty has always been systems for the rigs that go the distance: westfalia’s loaded for full time living, beefy land cruisers and compact overland rigs, vehicles where performance is paramount, and every square inch of space counts.

After years of designing and installing custom systems for dozens of customers and rigs, we took on the challenge of distilling these systems down into the best possible system, in the smallest footprint we could manage.

We’ve been working on The Crooked Box: A pre-wired, compact drop-in power system that can fit anywhere a battery fits, and will outlast the rig you put it in.

The Box is not a mobile charging station for your phone and fridge, this is a fully functional 12V auxiliary power system for your vehicle or camper, built to the same high standards we utilize for our custom installs. It includes a top-of-the-line lithium battery plus all the charging, monitoring, and fusing that we typically install in a custom installation.

We’ve been through multiple prototypes and versions and have settled on this one with a tough powder-coated aluminum box, aircraft grade hardware, and an easily removable access panel making the entire system serviceable.

If you are looking for the SMALLEST drop-in system on the market designed to run your entire adventure vehicle (and we’d challenge you to find a smaller custom install either), this is it. Final dimensions come in at 14” x 10.75” x 11” – barely bigger than an auxiliary battery, and this includes a lithium battery, DC-DC charger/MPPT solar controller (Redarc BDCD), battery shut-off switch, internal fusing, a Bluetooth battery meter, a blue sea fuse block with 12 pre-wired circuits to run your entire auxiliary power system, and a quick plug to support an inverter for those that want 110V power.

Now accepting pre-orders for our next batch.  Pre-ordering commits you to the next batch so all sales are final.  These are all be batch built, by hand, in our shop and are backed by the same commitment to quality we bring to everything we do. Slower Than Fast.

*NOTE: This item is currently available for shipping ground only*


  • Dimensions: 14” L x 10.75” W x 11” H
  • Battery Power: 100 or 120 Amp hours (AH) of lithium battery by Expion360 
  • Weight: 45 lbs
  • DC Charge rate (DC & Solar): 25A to 40A
  • Charge sources (input):
    • Alternator (integrated DC-DC charger)
    • Solar (integrated MPPT controller)
    • Single 50A Anderson plug for both input sources
    • External ground post for a single chassis ground
  • Output:
    • 12 pre-wired and fused circuits for all the DC accessories in your rig
    • 125A fused Anderson plug for an external inverter (inverter not included)
    • Maximum supported inverter size: 1200w (100A box); 1400w (120A box)
    • Integrated Bluetooth battery meter – view battery state of charge, current usage, and time remaining from a smartphone.
    • Battery kill switch
  • Features:
    • High quality aluminum enclosure designed and built in USA.
    • Aircraft grade hardware to ensure The Box lasts at least as long as the rig it’s in.
    • Small footprint means The Box can be mounted nearly anywhere you can fit a battery and can accommodate the tightest builds. We designed the box to fit under the bench seat in a Westfalia camper, or under the jumpseat in a weekender westfalia, but the small dimensions make it possible to fit The Box in virtually any build.
    • Easily removable cover to access all internal parts – infinitely serviceable.
    • Provided feet for floor mounting.
    • All inputs and outputs are easy to connect/disconnect making installation a breeze and making it possible to move The Box from rig-to-rig if you move on to a new platform.
    • Easy installation – run 3 cables to The Box : 12V input, Solar + and a shared chassis ground, and The Box is ready to go. Cut out hours or days of system design, planning, and fitting.
    • Monitor your system from the VictronConnect app to understand your available power, power usage, and time remaining.
    • Final Box version includes integrated handles.