The short answer. Lithium costs more up front and usually less over the years, because it lasts many more cycles. But a lead-acid battery that’s only used a few weekends a year ages out before it wears out, and then the cheaper battery can win. Put in your own quotes and how you use the boat to see which side you’re on.
Enter the two prices you were quoted.
Battery only. The charger, monitor and wiring a lithium bank needs are extra, and so is a lead-acid bank’s larger size for the same usable power. Guidance, not a substitute for a qualified electrician. On a boat, when in doubt, ask an ABYC-certified marine electrician.
Guidance, not a substitute for a qualified electrician. On a boat, when in doubt, ask an ABYC-certified marine electrician.
How it works
The tool needs two prices, and only you have those: type in what you were quoted for each battery at the same amp-hour label. We don’t show battery prices here.
Then it works out how long each battery lasts the way you use it:
- Lithium: Victron rates its LiFePO4 Smart battery for 2,500 cycles at 80% depth of discharge and 5,000 at 50%. Divide by your cycles a year and that’s its life.
- Lead-acid: Victron’s AGM Deep Cycle is rated for 400 cycles at 80% and 600 at 50%, gel for 500 and 750. But lead-acid also ages on the shelf: Victron gives AGM a float design life of 7 to 10 years at 20°C and only 4 at 30°C. The tool takes whichever runs out first, using the 7-year low end.
It counts how many of each you’d buy over the years you choose, and what you’d spend.
Two examples
Say lithium is quoted at $800 and AGM at $300 (example numbers, not ours). You live aboard on weekends and most of the summer, about 100 cycles a year, using 80% each time. Over 10 years the AGM lasts 4 years per battery, so you buy 3: $900. The lithium is still going: $800.
Now a boat that goes out 30 times a year and uses about half the battery. The AGM’s 600 cycles would take 20 years, but at 20°C it ages out around year 7. Two AGMs over 10 years: $600. The lithium: $800. Lead-acid wins that one, and the flagship page says the same: for light use, spend the money on a good charger and a monitor instead.
What the tool leaves out
- The parts around the battery. A lithium switch-over usually needs a DC-DC charger, a lithium-ready shore charger and a shunt monitor. See Upgrading a boat to lithium: everything around the battery, or the Boat lithium upgrade kit.
- Lithium’s calendar life. Victron doesn’t print one, so lithium life here is cycles only. A battery that sits for decades will age anyway.
- Usable amp-hours. At 80% the two batteries deliver the same amp-hours here. If you stop lead-acid at 50% to get its 600 cycles, you need a bigger lead bank for the same use. The Battery bank size calculator shows that gap.
Quick answers
Is lithium cheaper than lead-acid in the long run? For a battery you cycle often, usually yes, because Victron rates its lithium for 2,500 cycles at 80% depth of discharge against 400 for its AGM. For a lightly used boat, a lead-acid battery can age out first and cost less overall.
How many years does an AGM battery last? Victron gives its AGM batteries a float design life of 7 to 10 years at 20°C and 4 years at 30°C, or fewer if you use up their cycles first.
Why doesn’t the calculator show battery prices? Prices change and differ by size and brand. Enter the quotes you have and the tool does the rest.
Does this include the cost of a new charger? No, it’s battery only. A lithium upgrade often needs a DC-DC charger and a lithium-ready shore charger; add those to the lithium side yourself.
Sources
- Victron Lithium Battery Smart datasheet: https://www.victronenergy.com/upload/documents/Datasheet-12,8-&-25,6-Volt-lithium-iron-phosphate-batteries-Smart-EN.pdf
- Victron Gel and AGM batteries datasheet: https://www.victronenergy.com/upload/documents/Datasheet-GEL-and-AGM-Batteries-EN.pdf
