The desire to convert or expand our existing AGM setup to lithium in order to make ourselves more self-sufficient was right at the top of our list after moving on board. At first, however, the available options seemed either very expensive or complicated. But with a well-planned conversion, we managed to get it done relatively quickly and affordably.
The power supply of a bluewater/liveaboard boat
One of the biggest challenges when living aboard a boat is having a reliable power supply. For marina dwellers or for short day or weekend trips, that’s not really an issue, as you can usually use shore power. But as soon as you spend several days at anchor or are under sail for longer periods, power management becomes crucial.
Of course, you could simply run the engine to charge the batteries (technically accumulators). But that’s neither good for the environment nor practical: it burns unnecessary diesel—which on a small boat is only available in limited quantity (in our case, 106 litres in the tank + 30 litres in jerry cans)—and it’s noisy and smelly. Moreover, running the engine for long periods at anchor without any real load doesn’t do it any good either (keyword: glazing cylinders).
Converting AGM to lithium
So, the decision to expand or supplement our existing AGM system to become more independent had already been made early on. We had planned to replace the AGMs once they could no longer deliver the required performance. That happened sooner and more unexpectedly than we thought.
The old lead-acid system and its limits
Our original setup consisted of three 12V AGM batteries.
- 2 x 100 Ah connected in parallel as the service bank
- 1 x 80 Ah as the starter battery for the engine and the windlass
The batteries were charged either via shore power or through the engine’s alternator. When the engine was running, all three could be charged. The service bank and the starter battery were separated by a diode isolator. The problem with these is that you lose voltage (about 0.7V), and in the worst case, the batteries never fully charge, which can significantly shorten their lifespan.
Whenever we had shore power, the Mastervolt ChargeMaster 12/25-3 handled battery charging. There was also a small 50W solar panel permanently mounted on the sliding hatch cover, but it no longer worked.
On the consumer side, the biggest power users were:
- Fridge
- 2 laptops (charged via the service bank)
- 2 smartphones
- Router
When sailing, the laptops drop out of the equation, but we then add:
- Instruments (log, depth sounder, wind meter, etc.)
- Plotter and iPad for navigation
- VHF radio and AIS
- Autopilot
- Possibly navigation lights
At anchor, or when working and using laptops, we consume about 35–40 Ah per day. When sailing and running the autopilot, consumption can double or even triple (80–120 Ah), depending on how much the autopilot is working and whether navigation lights are needed.
Given that AGM batteries shouldn’t be discharged beyond 50% (11.8V remaining voltage) without reducing their lifespan, we effectively had around 100 Ah available for use—and that’s assuming full charge to start with. This would mean, at best, 24 hours at sea or two days at anchor. Not much, but enough to get us started, especially since we had already upgraded our solar setup (article coming soon!), which helped stretch the time between marina charges when the sun was shining.
For our planned crossing to Denmark, we estimated two days and one night at sea. That meant we would have had to recharge the batteries using the engine. On top of that, our Victron battery monitor showed worrying readings, leading me to suspect that at least one of the service batteries no longer had its full capacity.
The decision to go lithium (LiFePO4)
The timing for the switch wasn’t ideal, as we were anchored in Terschelling at that point. That meant every order had to arrive by ship, which took time, and every day in the harbour cost us 30 Euro. Naturally, that factored into our decision-making: it had to be quick to implement.
We had three possible options:
- Stick with AGM and expand capacity,
- Add lithium (LiFePO4) in a hybrid system, or
- Replace the AGM service bank entirely with lithium (LiFePO4).
Expanding the AGM setup
| Advantages | Disadvantages |
| Low cost | Requires substantially more space |
| Easy installation | “Wasted” capacity as only 50% dischargeable |
We only considered this option briefly. We simply didn’t have the space to install more AGM batteries on board, and it didn’t feel particularly “future-proof” either, since we didn’t yet know what our future consumption would look like.
Hybrid setup: adding lithium (LiFePO4) in parallel
| Advantages | Disadvantages |
| Easy to install | Very expensive |
| Space-saving | Limited scalability or capacity |
The simple “drop-in” option—like the BOS LE300 modules that expand AGM capacity with lithium—only came to our attention during the research phase. We seriously considered it for a while. But in the end, the high cost and slightly oversized dimensions for our available space ruled it out.
Replacing the AGM service bank with lithium (LiFePO4)
| Advantages | Disadvantages |
| Most capacity | High cost |
| Space-saving | Requires more installation work |
Ultimately, we decided on a full replacement of the AGM service bank with lithium batteries. This allowed us to fit the greatest possible “Ah” capacity in the existing space. Although the upfront cost was quite high and the charging infrastructure required adjustment, the system would be much more future-proof and upgrade-friendly.
AGM to lithium conversion: installation details
To keep the installation simple, we chose two 12.8V Lithium SuperPack batteries from VictronEnergy. They have an integrated Battery Management System (BMS) and can be connected in parallel. We replaced 2 x 100 Ah AGM with 2 x 100 Ah lithium, gaining the advantage of smaller size, roughly one-third the weight, and an effective usable capacity of about 180 Ah instead of 100 Ah.
However, the charging infrastructure needed a rethink. Having two different battery systems (lead-acid for engine start/windlass and lithium for service) complicates things. After some planning, we found a simple solution: we decided to sacrifice the “fast charging” advantage of lithium and kept our system largely unchanged.
Both the alternator and the shore charger now charge the AGM starter battery. That way, we don’t need to protect the 50A alternator from overload or sudden disconnection if the lithium BMS shuts down. This setup also allowed us to remove the diode isolator, ensuring full alternator voltage reaches the battery.
The lithium batteries are charged via a DC-DC charger (Orion-Tr Smart 12/12-30) connected directly to the AGM starter battery, which kicks in when the starter battery is being charged. It needed installing and proper fusing, of course.
In addition, we now have two independent solar installations with two charge controllers directly feeding the lithium batteries.
Feel free to get in touch if you’d like to see the wiring diagram.
Costs
Here’s a breakdown of the costs for the lithium battery installation:
| Item | Cost |
| 2 x 100 Ah VictronEnergy Lithium SuperPack | 1,950 Euro |
| 1 x VictronEnergy Orion Smart 12V|12V-30A Non-isolated | 280 Euro |
| Installation materials (cables, fuses, busbars, etc.) | 250 Euro |
| Total | 2,480 Euro |
Practical experience
For our current life aboard—working half-days, coastal cruising, 2–3-day passages and spending several days at anchor in summer—our current setup is more than sufficient. We’ve never really hit our capacity limits. Unless we’re far north (like Norway in 2025), we are energy self-sufficient at anchor in summer.
As we charge the lithium batteries through the DC-DC charger, the charging current is limited to the 25A output of our chargers (battery-to-battery and shore power). That’s not really an issue, as we regularly stop at marinas and usually stay at least one night—enough time for a full recharge. Our standard 50A alternator is also perfectly capable of maintaining that 25A continuously.
Looking ahead
Switching from AGM to lithium right away was definitely the right decision. Looking to the future, we’d like to add several upgrades to the boat that will significantly increase our power consumption—beyond what our current solar and battery setup can handle. On our wishlist:
- Electric outboard motor
- Watermaker/desalinator
- Multi-day sailing passages
- Electric cooking
Leaving electric cooking aside for now, as it’s lower on the list, this still means doubling our battery capacity at least, and expanding the solar array accordingly.