Why LFP is Better than AGM for Pontoons

Yes — but only if the LiFePO₄ starting battery is designed correctly (high-current BMS + alternator-safe).

If you drop in a proper LFP starter battery, it will outlast and outperform AGM in a pontoon.
If you drop in a cheap Amazon lithium with a weak BMS, you’ll trip the BMS or cook the alternator.

So the answer is conditional, not universal.

Why LFP is Better for Pontoons (Real-World Use)

Pontoon owners do this a lot:

• Engine off

• Stereo, fishfinder, lights, livewell pumps running

• Sometimes for hours

That is deep cycling behavior.
AGM starting batteries die early under that.

LiFePO₄ is designed for deep-cycle + partial-charge use.
It doesn’t sulfinate, and doesn’t care if it sits at 40–90% all day.

So yes — in real boating behavior, LFP wins.

BUT

There are two requirements:

1. The BMS must be starter-rated

• Minimum 200A–600A discharge capability

• Must not shut off during cranking
  (If it does → boat is dead in the water.)

2. Alternator charging must be safe

Pontoon alternators are low output (25–60A typical).
That’s actually good → less risk of overheating.

But the battery still must have either:

• Input current limiting in the BMS
  or

• A DC-DC charger between alternator and battery

If the BMS just hard-cuts when full → voltage spike → alternator diodes fry.

So: Charge current limiting matters.
Discharge C-rate does not protect the alternator.

Blunt Final Answer

Yes — LiFePO₄ is better for pontoons because pontoons deep-cycle their starting battery all the time. But you must use a starter-rated BMS and alternator-safe charge control. If those two boxes are checked, LFP lasts 3–5× longer and performs better.