Practical Boat Owner contributor Will Renilson of Beccles, Suffolk, had been looking to change to lithium batteries for his domestic battery bank after his 440Ah AGM (absorbed glass mat) domestic battery bank failed for a second time aboard his Jersey 36, Jersey Lass.

He said: “I’ve been especially careful with my usage versus charging regime after losing the battery bank the first time but now it is gone again after less than two years. It’s quite frustrating as they’re very expensive batteries.”

Will’s Jersey 36, Jersey Lass

Will contacted his insurer and was told changing batteries, particularly to lithium-ion, ‘would impact cover’ unless the changes were agreed by the insurer and met an extensive list of requirements.

Although lithium-ion batteries are used in smaller watercraft or are sometimes fitted by DIY-ers, using repurposed lithium-ion car batteries, most boat owners opt for Lithium-Iron Phosphate (LiFePO4), which is much safer. The LFP cells are nearly fireproof, although any battery can cause a fire if fitted incorrectly.

“I was told that a spate of claims regarding boat battery fires over the last 18 months has prompted many insurers to tighten their requirements for policyholders,” said Will.

“The underwriter said lithium-ion batteries will impact the cover unless the insurer has agreed all the details including: where the batteries have been manufactured; whether they are new; kept in a controlled and protected environment; how the charging is undertaken and monitored; if the charge occurs overnight; whether appropriate fire extinguishers are kept close by (as foam and water extinguishers will not work against these types of fires); where batteries are stored; confirmation that unused batteries will be kept in a sealed protective fireproof box; what fire protections are in place when charging to ensure no charge fluctuations occur which can lead to overheating fire and thermal runaway; and whether charging occurs on the vessel or onshore; and what protections are in place to ensure no water contamination which can lead to thermal runaway.”

A new switch will disconnect charging of the domestic bank in Will’s bid to extend battery life after his AGM batteries lasted only two years

Switch wired via a solenoid will light up when batteries are charging

Lithium batteries: expert view 

Will also spoke ‘in depth’ to PBO engine expert Stu Davies and the teams at Eco Bat and Trojan, as well as his marine engineer, and while still tempted by lithium batteries, the “hideously expensive” price means he will instead “try Trojan lead acid batteries and change my usage and charging methods.”

A spokesperson for boat insurers Navigators & General said: “We recognise that lithium-ion batteries have advantages and disadvantages.

Navigators & General has produced a helpful guide to help boat owners understand the risks associated with these and help them make informed choices. We would always recommend customers contact their insurer or insurance broker to discuss any changes before starting any work so they can ensure they have the appropriate cover in place.”

A spokesman for Haven Knox-Johnston (HK-J), which has also published lithium-ion battery guidance online, said: “Insurers are starting to build up changes to policy wordings which will be implemented in the future. These are not yet 100% crystallised and the affect on premium is, as yet, unknown. We hope the changes brought in are sensible and proportional to the risks and we’re working closely with the industry to try and ensure a smooth transition as we do not want to stop people doing their bit for the environment.”

Free webinar

HK-J is holding a webinar with experts to set out some facts about lithium batteries, on Thursday 23 November. Register at: Tinyurl.com/HavenKJWebinar

The spokesman added: “We hope to be able to clarify subjects such as installation and safe usage to try and ensure a much safer future in this area.”

Adam McMenemy of ACM Marine, based in Emsworth said: “I’d advise boat owners looking to switch to lithium batteries to get a marine electrician to do any installation. There was a guy at the marina who did a DIY installation and damaged £4,000-worth of lithium batteries because he put the incorrect regulator in.”

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Coastguard guidance

In a Marine Guidance Note (MGN) published in June 2023, the UK’s Maritime and Coastguard Agency (MCA) said: “There has recently been an increase in the number of fires on yachts, with industry groups estimating 16 total losses due to fire between August 2021 and August 2022; whilst the source of some of these fires are explained and have no relation to the measures proposed in this guidance (for example arson, collateral damage from another fire, etc.) around half have not had their cause established yet; one potential explanation for the unexplained fires, out of many potential causes, could be lithium-ion (Li-ion) battery fires.”

The MCA advises that new designs of yachts should make provisions for the safe charging and stowage of such electrical supplies, to increase safety for handling, charging and stowage of Li-ion batteries and craft with these in-built. It advised that all batteries over 100 Wh for use with electric vehicles should be subject to storage requirements outlined in the MGN.

This article has been updated to reflect the fact most boats tend to be fitted with Lithium-Iron Phosphate (LiFePO4) batteries.