Lithium House Bank Safety

How to keep your batteries (and boat/home/life!) safe with lithium iron phosphate house batteries

I write this as we sit in Guna Yala (San Blas) Panama, after reading across multiple WhatsApp Groups that another catamaran caught fire here today (another, Life of Pi, burned and sank a few weeks ago).

Today's tragedy with "Terra" is suspected to have been caused by the Lithium House bank overheating during charging, starting on fire, at which point there are moments, and very few ways, to safely extinguish that fire.  

Once starting on fire, stopping that fire is exceptionally difficult; the better plan is to take all possible precautions to prevent the batteries from being abused, which is what commonly leads to these tragedies.  While sailors never intend to abuse their house bank, improper settings, poor wiring and inferior components can lead to this happening to the most well intentioned.

What are LiFePO4 Batteries

Lithium Iron Phosphate batteries are the current, best technology for high capacity energy storage and the technology/chemistry used for all mainstream "Lithium" house bank batteries. While there are other technologies on the market, (Carbon based, etc), they are not widely deployed.

Lithium Polymer batteries, like those in smart devices, cameras, drones, etc, are considerably more likely to catch fire, however, their size allows them to be pitched overboard should a fire start.  As a general rule of thumb, these batteries, especially if larger in size, should not be charged un-attended on a boat.

The composition of LiFePO4 batteries makes them less likely to fail from thermal run-away (where the heating, only causes the failure to intensify). 

How LiFePO4 Batteries Get Abused

• Overcharging (Too much current or voltage applied)*
  This is the most damaging and can result in fires.
• Battery temperature becoming too high, especially while charging or discharging*
• Allowing the battery State of Charge to get to low (<10-15%).*
  This will result in a noticeable decrease in battery lifespan, but should not result in a fire.
• Physical damage to the battery cells (Impact, severe vibration, etc.)
  This can causes the layers (think of a Swiss roll, which is how each cell is constructed) that make up the battery to contact one another, which results in a partial short internally, which results in heating and then more heating and then fire.
  Drive a nail through any Lithium battery and it will almost assuredly burst into flames.
• Battery cables that are substantially too small for LiFePO4 currents or loose connections.
  This can indirectly heat the battery through the cable connection.
  This is something that must be carefully evaluated when upgrading from lead-based batteries (Lead Acid, AGM, Lead Carbon, etc), as those batteries can deliver a fraction of the current that similar capacity Lithium based batteries can.
• Manufacturing Defects
  Cheap batteries, built in a non-ISO 9000 factory, are a substantially higher risk.
  Plain and simply, this is not the place to find the cheapest option.
  Top quality batteries are the safer way to go. (Victron SmartLithium, Battle Born, ReLION, Epoch to name a few)

* - Several of the bulleted items above are tagged with an asterisk.  All of these potential sources can be all but eliminated by a proper BMS, preferably internal to each battery module and one system-wide BMS. It is the belief of the author, that battery units that do not have an internal BMS should never be used, let alone on a boat.

How to Prevent LiFePO4 Abuse

• Don't let them get too hot!
• Placing them in an engine compartment or generator compartment should be avoided at all costs.
• Add ventilation to the area in which they are fitted - We use a temperature controlled fan to turn on when the battery compartment on Mira gets above 35C.
• Make sure they can not get discharged at too fast a rate - See External BMS
• Make sure that every device that can charge the house bank is properly configured!!
  This includes, Chargers, Inverter/Chargers, MPPTs, Wind Generators, Alternators, Hydro-generators.
  Every quality Lithium battery will come with a spec sheet showing at least the following key values:
  Charging Voltage (To get to 100% full) - typically 14.2/28.4/56.8V
  Absorption Voltage (To maintain that charge without adding extra heat) - typically 13.5/27.0/54.0V
  Maximum Charge Current - typically 0.5C
  Suggested, Normal Discharge Current (for best battery lifespan)- typically 0.5C
  Maximum Continuous Discharge Current (to prevent overheating)- typically 1.0C
  Peak Continuous Discharge Current (to prevent overheating from very short peaks) - typically 2.0C or more
• Try not to allow them to discharge to more than 20% SOC!
  This is more about battery lifespan, as opposed to fires.
  Battery State of Charge for LiFePO4 batteries is always a calculation/estimation by integrating charge into and out of the battery.  That estimation may be off by some amount, so while the battery can handle going to 10% SOC, the number you see on your SOC meter may be off, so it is better to err on the side of safety.
  What you can be sure of is that the battery voltage should never be allowed to drop to 12.0V /24.0V/48.0V(which is about 9% SOC)
• Make certain that all battery cables are of adequate size!
  This can be harder to generalize, however for a 12V system, the battery cable size often needs to be 2/0, 3/0 or 4/0, (70mm², 95mm² 120mm²).  For large battery voltages, the gauges can sometimes be reduced, but large house banks at higher voltages may still require large cables.
  The Victron Toolkit app can be very helpful to determine proper wire sizes.
• Make sure that all battery connections are tight!
  A loose connection can result in heating, which can translate to the battery heating or just cause a wire fire on its own.
  For these large gauge wire connection, you should not be able to budge them at all with your bare hands. Ideally, find the torque spec for the connector in question and do it right!
  Add this to your list of quarterly inspections.
• Make sure all battery cables are routed such that chafe to the wires can not occur!
  I have seen at least two installations where the battery cable connection was tightened such that, given enough time, it would have chaffed through the insulation and caused a battery short. An internal BMS should catch this, but that surge would be huge and its unknown if the internal BMS would be able to react fast enough to prevent heating and thermal runaway.
• Inspect for damage and replace
  Add battery inspection to your quarterly checks. If any damage occurs that is more than cosmetic, replace the battery. Yes, they are very expensive and maybe the battery is fine, but your boat is expensive too and your life is priceless.
• Add an External BMS
  There are several companies that make external BMSs (Battery Monitoring Systems).  Their job is to make sure that the internal BMS in the battery never needs to do anything.  You can think of this as redundancy.
  I am most familiar with Victron Energy products, and they have great offerings for just about every need, but others exist from other companies as well.  
  All boat power routes from the batteries through the External BMS.  If that BMS sees something out of whack, it isolates the battery bank immediately.
  They can be expensive but consider it like insurance.  You pay it hoping you never have to use it!
  Since all batteries route through this BMS, overall system amperage can be monitored and acted upon to disconnect the entire system.  You can usually also wire in a small switch to force an immediate dis-connection.  In contrast, the internal BMSs in the batteries only see the current going into one battery module.

What to do if there is a fire

Lithium battery fire are exceptionally hard to contain. They burn violently and they burn until they have used all of their internal storage energy or until they are sufficiently cooled. They also release toxic fumes and if those aren't venting, you are not going to be able to stay near the burning batteries.

If you should have a Lithium Battery Fire, the first thing that should be done, IF QUICK AND EASY TO DO, is electrically disconnect the battery from the boat.  This can be a battery on/off switch, or it can be an external BMS remote switch. Much of the heat will come from thermal runaway, which removing external power will do little to solve, but if it's easy, disconnect the battery bank.

If the fumes are heavy or your path to leave the boat is in jeopardy, grab essentials and leave the boat.  You have a few minutes to control the fire and then you will not be able to do enough to stop the fire.

In that first minute, your objective is to prevent the boat from catching fire, as you will likely not have enough fire extinguisher to actually put out the lithium batteries.  Copious amounts of water could be used to drench the battery and surrounding areas, but lithium batteries will continue to burn fully submerged.

IF YOUR SAFETY IS EVER IN JEOPARFY, LEAVE THE BOAT, you changes of extinguishing the fire are unfortunately small.

Summary

LiFePO4 batteries have revolutionized the way we can life on a boat.  Their storage capacity, energy density, weight and charge rate abilities are light-years ahead of all lead-based technologies.  High quality battery modules are inherently safe and a handful of best practices can be followed to make them even safer.  With even the safest technology, accidents and one-off problems can still occur.  In that unlikely event, there is a very high likelihood that you will have to abandon ship.

Next Steps

Please take the information above and double check the important items that you can. 

If you are physically near me, I can check setting and wiring in person. If you have a Cerbo GX / Ekrano GX with internet access, I can check all of your system settings remotely.  I like to do this as a free service and if I find nothing that needs attention, I don't charge.  If I find anything that I feel should be adjusted, I will bring it to your attention and let you decide what to do.

If I can be of service, reach out via email: mike @ OnANewTack.com (Spaces added and no link to prevent spam). 

You can also reach me on WhatsApp: +1 nine-one-nine 412 7058