The Offshore Voyaging Reference Site

Lithium Batteries Buyer’s Guide—Part 1, BMS Requirements

So we have carefully thought about the tradeoffs after reading this chapter (where I cut through all the fanboy crap to what really matters), and decided that lithium batteries are the way to go for our offshore voyaging boat.

And we have figured out how much usable battery capacity we need and which charging sources and output power are required to keep up with our usage, as well as whether our system will be 12 or 24 volt, all covered in earlier chapters in this Online Book.

Now what? What gear should we actually buy?

Sure, we can dive into a hundred YouTube videos, but most are by someone who has never, or rarely, been offshore voyaging, and, worse still, many of the presenters could not explain ohms law1 if their lives depended on it—being a great presenter can mask truly stunning ignorance.

Or we can read who knows how many manufacturer web sites, reviews, and/or videos claiming that one particular lithium battery and BMS is best, or best for the money. But how do you decide who is making sense and who is full of shit and/or just trying to make a sale?

And even if we can figure that out, there is no best, there is only best for each of us.

To solve these problems I’m going to explore how each of us can develop our own set of buying criteria so we can cut through the noise to find and buy the best system for us.

The key points that are vital to understand are in the blue (tip) and pink (alert) boxes; that said, it will make more sense if you read the whole article carefully.

Also, I have used photos of various equipment to illustrate the article, but that does not mean I’m specifically endorsing that piece of gear.

What Matters To Us

The absolute number-one thing we need to fix in our minds before we go any further down this lithium-battery system selection road is that the needs of offshore voyaging boats are different and more stringent than pretty much any other usage case except aircraft.

Don’t Look To RVs (Campers)

For example, a system designed for a recreational vehicle (RV) is useless on an offshore voyaging boat because:

  • Lithium-battery system load dumps on an RV don’t result in the power steering shutting down (think autopilot), the headlights going dark (think nav lights), and the dials blinking out (think plotter and instruments) in the middle of the highway.
  • RVs generally spend a lot more of their time under power and have more room for solar panels in relation to their needs—an RV is more like a motorboat than sailboat.
  • Most RV campers spend a lot more time on shore power.

RV lithium-battery systems do not supply mission-critical safety systems (driving), offshore voyaging boat systems do.

It’s also important to understand that RVs are a far bigger market for lithium-battery systems—for example, less than 10% of Wakespeed WS 500 alternator regulators are sold to boat owners—so most of the documentation and suggested configurations we find on the internet do not apply to us.

Compare Against a Benchmark

Next we need to compare against the long-proven solution, a well designed and installed lead-acid based system, and be realistic about what we are taking on when we leave that behind:

  1. Installing a lithium system that increases the chances of an electrical blackout is bad seamanship.
  2. Lithium systems are way, way more complex and intrinsically less reliable and fault tolerant.

If we install a lithium-battery system that’s anything less than done right, we will have taken a huge step backward. The ocean doesn’t give a shit how cool our electrical system is, it only cares about how functional and reliable it is.

Good News, Bad News

The good news is that today we can build a lithium battery-based electrical system that’s makes the offshore voyaging boat grade, and even do that at a relatively reasonable cost.

The bad news is that it’s on us to figure out how to do that in a seamanlike way, since there are no turnkey systems specially designed for our needs.

Actually, there are from Ocean Planet Energy, but even if we decide to buy the whole system from Bruce and his good folks (highly recommended), we still need enough understanding to know what he’s talking about, and to install and maintain the system right; yes, even if we pay someone else to do the actual work.

Why I’m Writing This

But, before I dig into the technology, this article and how it will unfold was, as happens so often, inspired by a member comment:

Right now my hang-up is why LFP communication with the Alternator Regulator is necessary, and I have heard no reasonable technical explanation from anyone yet.

Member, Rick

I have to say that when I first read that I was a little put out. After all, I have written a complete Online Book, much of it explaining just that in detail. If you are too lazy to read it…yada, yada, yada…

But then I realized Rick has a point:

  1. I need to explain this more simply and in one place, rather than scattered throughout the Book.
  2. I also need to come up with a solution for those who don’t want to go that far or already have lithium batteries that don’t communicate; often, but not always, called “drop in”.

And then, once we have covered that off, we need a simple, or as simple as it’s possible for me to make it, list of criteria we can use as we buy stuff.

By the way, if you were wondering why there was no article or tips last week it was because I spent a ton of time researching for this article—this stuff is still complicated!

Let’s 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