Using Lithium Iron Phosphate Batteries to Repower
Anyone interested in replacing their marine batteries should read the story of catamaran owners who recently repowered their boat. They replaced their AGM deep cycle batteries with marinized lithium iron phosphate batteries – for a lot of good reasons. Lithium iron phosphate batteries outperform lead-acid across the board:
- Charging efficiency – Lithium accept charge much more quickly – without having to slowly charge the last 15 – 20% typical of lead acid. Kill your generator sooner!
- Discharge efficiency – Unlike lead acid (AGM, gel, or wet cell), lithium batteries can be discharged quickly without heating excessively and losing much of their rated amp-hour capacity.
- Depth of Discharge – Lithium batteries can be routinely discharged to 70%, versus 50% for lead acid batteries.
- Internal resistance – Lithium batteries are highly efficient, returning nearly the same number of amp-hours as were required to charge the battery.
- Storage – Similar to AGM, lithium iron phosphate batteries have very low self-discharge rate, allowing long-term battery storage without concern for the batteries going flat.
- Stable output – Lithium batteries maintain their full nominal voltage, even when being heavily discharged – until they're 70% discharged.
- Expected life – Lead acid last approximately 1,500 cycles if they're not discharged beyond 50% too often, while lithium claims 5,000 cycles at 70% discharge.
- Cost – Lifeline AGM were priced at $3,600 with 252 usable amp-hours, versus Winston lithium batteries, which cost $2,365 and provide 280 usable amp-hours.
- Weight – The lithium deep cycle battery bank weighs 157 pounds (71 kg), while the AGMs they replaced totaled 423 pounds (192 kg).
- Environmental – Lithium batteries are far less toxic than lead acid batteries.
- Safety – Lithium batteries don't generate flammable gasses while charging. Perhaps of interest – you can watch a LiFePO4 battery being cut and crushed while still powering a light.
The downside is that you need to have an effective battery management system which both limits the voltage while charging and shuts off loads if the voltage while discharging drops too low. Violating either of these rules can substantially reduce battery life.
If you're interested in reading a bit more about lithium iron phosphate batteries, there's a thread at cruiserforum you can peruse – or you can fire up your favorite search engine.
I'm still just thinking about installing lithium iron phosphate batteries, but they look good from here!