The Offshore Voyaging Reference Site

Building a Seamanlike Lithium Battery System

The electrical system on an offshore voyaging boat must:

  • Have no potential for a sudden blackout of electrical power (load dump).
  • Require little human supervision for reliable operation.
  • Place no added stress on the skipper and crew, particularly when the chips are already down.
  • Be fault tolerant: will keep supplying power even after a hardware or software failure.

If those requirements don’t make sense to you, please read, or reread this article.

Now that we have the requirements defined, it becomes clear that, due to intrinsic fragility and level of complication, no lithium-based system available today can satisfy all of the above requirements without a backup system.

The good news is that there is a simple and relatively inexpensive solution to the problem:

The Requirements

To make a lithium-based system truly ocean ready, it must have a backup that:

  1. Is simple and easy to understand.
  2. Will take over critical loads instantly with not even a millisecond blackout. (Read or reread this article if that did not make sense.)
  3. Does not rely on complex hardware and software for operation.
  4. Allows the skipper and crew to keep operating the boat safely for several hours after a main system failure until there is a good time, without a lot of other stuff going on, to investigate the problem.
  5. Will supply critical loads for several hours while the main system is being fixed.
  6. Will get us home if the main system can’t be fixed at sea or in a remote place.

The above list of requirements makes it obvious that the backup should be based on good-old simple and tried-and-proven lead-acid batteries.

It makes no sense to back up a complicated lithium system with another complicated lithium system, when we can design a better backup for less money using a lead-acid battery.

Let’s dig in to how to do that:

More Articles From Online Book: Electrical Systems For Cruising Boats:

  1. Why Most New-To-Us Boat Electrical Systems Must Be Rebuilt
  2. One Simple Law That Makes Electrical Systems Easy to Understand
  3. How Batteries Charge (Multiple Charging Sources Too)
  4. 5 Safety Tips For Working on Boat DC Electrical Systems
  5. 7 Checks To Stop Our DC Electrical System From Burning Our Boat
  6. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  7. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  8. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  9. Balancing Battery Bank and Solar Array Size
  10. The Danger of Voltage Drops From High Current (Amp) Loads
  11. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  12. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  13. Battery Bank Separation and Cross-Charging Best Practices
  14. Choosing & Installing Battery Switches
  15. Cross-Bank Battery Charging—Splitters and Relays
  16. Cross-Bank Battery Charging—DC/DC Chargers
  17. 10 Tips To Install An Alternator
  18. Stupid Alternator Regulators Get Smarter…Finally
  19. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  20. Smart Chargers Are Not That Smart
  21. Replacing Diesel-Generated Electricity With Renewables, Part 1—Loads and Options
  22. Replacing Diesel-Generated Electricity With Renewables, Part 2—Case Studies
  23. Efficient Generator-Based Electrical Systems For Yachts
  24. Battery Bank Size and Generator Run Time, A Case Study
  25. A Simple Way to Decide Between Lithium or Lead-Acid Batteries for a Cruising Boat
  26. Eight Steps to Get Ready For Lithium Batteries
  27. Why Lithium Battery Load Dumps Matter
  28. 8 Tips To Prevent Lithium Battery Black Outs
  29. Building a Seamanlike Lithium Battery System
  30. Lithium Batteries Buyer’s Guide—Part 1, BMS Requirements
  31. Lithium Batteries Buyer’s Guide—Part 2, Balancing and Monitoring
  32. 11 Steps To Better Lead Acid Battery Life
  33. How Hard Can We Charge Our Lead-Acid Batteries?
  34. How Lead Acid Batteries Get Wrecked and What To Do About It
  35. Equalizing Batteries, The Reality
  36. Renewable Power
  37. Wind Generators
  38. Solar Power
  39. Watt & Sea Hydrogenerator Buyer’s Guide—Cost Performance
  40. Battery Monitors, Part 1—Which Type Is Right For You?
  41. Battery Monitors, Part 2—Recommended Unit
  42. Battery Monitors, Part 3—Calibration and Use
  43. Battery Containment—Part 1