Lithium has gone from exotic to ordinary on boats in the space of about five years. Prices have come down, the marine-specific options have multiplied, and most people asking us about them now aren't asking whether to switch — they're asking what they'll need to change to make it work.
It's a fair question, because a lithium battery isn't a drop-in swap for lead-acid in every installation. Here's an honest look at what genuinely improves, what it costs, and what else on the boat has to change.
The difference that matters most: usable capacity
This is the one that catches people out, and it's the reason a lithium bank of the same nominal size feels dramatically bigger.
A lead-acid leisure battery shouldn't routinely be taken below about 50% of its rated capacity. Do it regularly and you'll shorten its life considerably. So a 200Ah lead-acid bank realistically gives you around 100Ah before you're doing damage.
A LiFePO4 battery of the same 200Ah rating will happily give you the great majority of that capacity, cycle after cycle. In practical terms you're getting close to twice the usable energy from the same headline number — before you've considered anything else.
That's why people who switch often find they can go smaller on paper and still end up with more available power.
Weight and space
Roughly speaking, LiFePO4 comes in at around half to a third of the weight of the equivalent lead-acid bank. On a small craft, or anywhere the batteries sit high or aft, that's a meaningful change to how the boat sits and handles — not just a number on a spec sheet.
It also opens up installation options. Lead-acid needs to be upright and ventilated. Lithium is far more relaxed about orientation and doesn't off-gas in normal use.
Charging: faster, but your charger needs to keep up
Lead-acid has a nasty habit of accepting charge more and more slowly as it fills, which is why that last 20% seems to take forever on the engine or a generator.
Lithium accepts charge at a high rate almost all the way up. If you're running a generator or charging off the engine, that's less time listening to it.
The catch: your charger has to be able to deliver a lithium profile. An old lead-acid charger will either refuse to charge properly or, worse, apply an absorption voltage that isn't doing the cells any favours. Budget for a compatible charger as part of the job, not an afterthought.
Charging off the alternator needs thought too. A lithium bank will happily pull everything an alternator can give, indefinitely, in a way lead-acid never did — which can cook an alternator that was never specified for that duty. On anything beyond a modest bank, this needs proper regulation.
Lifespan and the real cost
The sticker price is higher. The cost per usable cycle usually isn't.
A decent LiFePO4 cell is generally rated for several thousand cycles, against a few hundred for a quality lead-acid battery. If you're a seasonal user doing a handful of cycles a month, you may well not replace a lithium bank in the time you own the boat.
The honest caveat: if your boat sits on a mooring, gets used a dozen times a summer, and has a battery bank that's coping fine, the payback maths is a lot less compelling than it is for a liveaboard or a boat with real electrical demand.
Cold weather is the one genuine limitation
LiFePO4 must not be charged below freezing. Discharging in the cold is fine; charging isn't, and doing it will permanently damage the cells.
For most UK boats laid up over winter with the batteries disconnected, this is a non-issue. If you're leaving a bank on charge in an unheated space through a North East winter, it matters a great deal.
Two ways round it. A good battery management system will simply refuse a charge when the cells are too cold — protecting the battery, though it does mean no charging until things warm up. Or you choose a battery with integrated heating, which draws a little power to bring the cells up to a safe temperature before accepting charge. The Renogy Pro Deep Cycle with Bluetooth and heating is built for exactly this.
What we stock
For most sailing and motor boats on a 12V system, Victron's LiFePO4 12.8V 200Ah Smart is the sensible default — well supported, Bluetooth monitoring, and it integrates with the wider Victron ecosystem if you're building out a proper system.
Moving to 24V, the Victron Lithium NG 25.6V 200Ah covers larger installations.
For smaller craft — tenders, day boats, electric-drive dinghies — the Rebelcell 12V80 Pro is a well-made compact option at around a kilowatt-hour.
And if you've already got a lithium bank and simply need more of it, the BOS LE300 extension battery is designed to add capacity to an existing setup.
Worth a conversation first
Battery swaps are one of those jobs where the battery is the easy part and the charging system is where the money and the mistakes live. If you're weighing it up, come and talk to us before you buy — it's a five-minute conversation that occasionally saves someone from a very expensive alternator.
Marine Chandlery, Unit G4 Narvik Way, Tyne Tunnel Trading Estate, North Shields.
