Lithium Batteries and Thermal Runaway

What is a thermal runaway? Insurance companies and lithium batteries, Victron Battery Management System

...Want to buy cheap? Think twice with Lithium batteries. Can't say you now haven't been warned.

Lithium Battery & Thermal Runaways

A thermal runaway lithium battery fire is up there with uncontrolled gas fires, as one of the worst-case fire scenarios on a small vessel.

While most fires have some form of management or fire control, a lithium thermal runaway battery fire does not.

Today’s batteries, whether it be lead-acid, AGM or Lithium are all very safe as long as manufacturer guidelines are strictly complied with.

Buying Lithium Batteries

Lead-acid and AGM batteries are well tried and tested, with most of their ventilation and fire challenges being well documented.

The challenge with lithium batteries is the myriad of cheaper lesser known lithium brands now coming on the market via social media to private buyers, bypassing reputable retailers.

We need to remind ourselves that reputable retailers have a lot to lose if their recommended batteries fail (including lawsuits from Insurance companies), so they have normally done their homework and carry reliable home-grown warranties.

electrical cabling

Is a Thermal Runaway a fire?

Lithium batteries currently fall in the Class B fire category, which means that the standard ABC fire extinguisher can be used.

This, however, is no use if there is a ‘thermal-runaway’ situation within a lithium battery bank.

Thermal runaway fires are extremely difficult, if not impossible, to stop or extinguish.

A simple Google search about lithium thermal runaways will highlight the record so far in the aviation sector, where fires present a particular problem, their lithium cargo record being far from positive.

Legal Liabilty

Recently chatting to someone who had built their own lithium battery bank from imported cells, we found them ill-prepared for a thermal runaway. Their cells had no protection.

So where does it leave a private person like you and me? Risk verse Reward.

If an incident occurred, would the Insurer come to the party? I doubt it very much.

victron battery management

Insurance Warning

There are incidents and aircraft hull losses caused by thermal runaways in freight loads of lithium batteries.

Technology today also have records of thermal runaways on smaller lithium powered portable devices such as mobile phones and laptops. So, it certainly does occur.

It is, however, the lack of control of a thermal runaway that is raised in this article.

In particular, if you (a private individual) are the importer and are bypassing a professional supplier and/or installer.

Check with your Insurance company, you may find your insurance is void by installing your own lithium. Surveyors will ask you too...we got asked.

So what is a thermal runaway?

A thermal runaway is an unstoppable internal chain event, where a cell or part thereof very quickly reaches high temperatures. The causes are varied but include internal mechanical or thermal cell failure and short-circuiting deep inside the battery.

Due to the short-circuiting, heat is generated by this single defective cell. The enclosed heat source self-generates to much higher temperatures.

The very hot defective cell core becomes unstable, having no way to release heat except to the enclosed surrounding cells thermally inside the battery. The surrounding cells then join in the masquerade and the battery very quickly heats from the inside out, which they term a thermal runaway.

Meanwhile little can be seen at the battery surface. This all happens very quickly, taking minutes to self generate to a point where the battery becomes extremely hot.

Common cues and/or senses used in picking up most other fires include sight, sound, aural and touch (the latter normally being a result of the first three). With early signs of a thermal runaway situation, however, we only have the sense of touch.

With smaller portable devices, lithium thermal runaways/fires are easily remedied…toss it into the ocean.

Vessel lithium batteries used in house banks are normally tucked away somewhere in some very secure robust area. So when it's finally realised that there is a problem, and then questioning if it's battery-related, who would think of touching or even want to touch a battery to resolve a lithium battery fire problem?

Thermal runaways happen quickly (as in minutes) and can get out of hand very quickly. 

From a ‘Proactive’ Thermal Runaway Point-of-view

  • The pressing challenge though is by the time a lithium fire is recognised, all hell would have broken loose in the confined vessel battery area. The suspect heavy battery/ies would possibly be too hot to touch and would more than likely have affected the adjacent batteries, making the situation even worse.
  • It's here that good quality, well-known lithium brands, or lithium battery vendors stand out. The better battery brands have tried and tested small inbuilt processors that can detect a cell problem (and other internal battery malfunctions) at a very early stage, isolating cells before they get to a point of a thermal runaway.
  • Our Victron batteries have lithium battery technology that sadly comes at a price. They do however supply comprehensive datasheets that clearly state ‘our LFP (lithium-iron-phosphate) batteries have integrated cell balancing and cell monitoring’.
  • They continue by saying ‘the cell balancing/monitoring cables can be daisy-chained and must be connected to a Battery Management System’ (
  • With the Victron Battery Management System, the unit ‘generates a pre-alarm whenever the voltage of a battery cell decreases to less than 3.1V (
  • The upshot here is that Victron (and a few other brands) have introduced additional cues to warn us of impending issues, which include thermal runaways.
  • on mySerenity
    We have a 1000-Ahr lithium battery bank tucked away under a bed in a room, which is difficult to get to at the best of times. However, we are very conscious of possible lithium battery thermal runaway and have planned procedures specifically for this scenario in our Crew Manual.
  • Proactive Warnings:
    To help warn of a thermal runaway, the Crew Manual states 5 indicators, most controlled via a quality Battery Management System (BMS).
  • 1. Complete electrical shutdown (via BMS),
  • 2. An aural alarm (via BMS),
  • 3. Touch (fire gloves in that electrical room for this purpose, and other reasons),
  • 4. Partial mains electrical shutdown (by way of programming the BMS), and
  • 5. A quality Battery Management System that relays a text to a mobile phone (when within mobile range), and a loss of Main Electrical power has occurred.
  • the 'take-home' here
    The key to our system is a quality Battery Management System (BMS), quality being the operative word.
  • Cost-wise - a proactive approach to a thermal runaway far outweighs the reactive approach of a suppression fire system that may not work with a thermal runaway on a sailing catamaran such as ours.
  • A Class B fire extinguisher (recommended) will do very little to reduce an internal self-generating thermal runaway lithium battery heat source in many small vessel house banks. So we really rely on the inbuilt battery processors doing their job.

From a ‘Reactive’ Thermal Runaway Point-of-view

  • There are fire suppression systems that could be possibly be used, however, install position and cost is eye-watering. It too uses fire retardant to flood the battery area, some use water that needs to be turned over constantly with more cold water. Can this reactive approach to extinguishing a thermal runaway on a small craft be justified?
  • The crew would correctly use the first fire extinguisher and start placing retardant on the battery area, providing a false sense of security that they doing the right thing. In fact, it could place the crew at a disadvantage in many ways. 
  • A good Vessel Manual provides clarity for all crew, following simple, short read-and-do procedures, and makes exceptionally good safety sense in this particular situation. Having an idea on how to tackle any fire on board a vessel, let alone a thermal runaway, while expecting the crew to be mind-readers, will not be too successful. 
  • we take this VERY SERIOUSLY
    If you are keen to improve your procedures but it looks all too hard, click here and scroll to the bottom of the page to our Crew Manual (search Index - LITHIUM FIRES) for some ideas on how we tackle this issue.
  • Be armed with your information, ask questions and do your homework very well if you are venturing off into Lithium on your own.
  • We have since sold our generator, we don’t use shore power, and have got rid of the gas system (except for the obligatory BBQ). It’s all running from Lithium powered by solar and have been extremely happy three years on.
  • There are very good quality lithium battery suppliers out there. Do your homework and stay safe.
  • This is an ‘unqualified research and observation article’ from 2020, and would warmly welcome any feedback from those more qualified in this prickly area to help provide a cost-effective approach to the challenge facing budget-conscious cruisers and thermal runaway situations.
  • Want to see our Lithium Batteries REAL-TIME, Click Here.
  • While I wish I was, I am not endorsed or sponsored by any products mentioned in this article...James (updated Feb 2023). 


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