Lead-acid is not one voltage
Battery University BU-403 describes charging flooded, gel, and AGM with constant-current / constant-voltage stages and different absorption and float windows. Gel sits lower than many flooded programs. AGM is not flooded with the caps glued on. A charger left on the wrong chemistry will undercharge one pack and dry out another. We read the DIP switches or the app before we blame the battery.
Lithium is a stop, not a float
BU-409b sets LFP at 3.65 volts per cell, about 14.6 volts on a 12-volt pack, and no float. Those figures are a published LFP example; the pack maker’s charge profile is what we set on the boat. A leftover flooded or AGM program is not that profile. Some BMS units tolerate a lead charger for a while. Tolerate is not a charge algorithm. If the pedestal cannot be reprogrammed, the charger is on the quote with the batteries.
Multi-bank units still have one brain
A three-bank bass-boat charger may use one chemistry setting for all banks. Mixing a lithium bow with flooded starting on that unit is how one chemistry gets the wrong finish. Separate chargers, or a unit that can assign profiles per bank, are the adult options. We do not guess the firmware from the color of the case.
Temperature compensation
Some marine chargers lower voltage in heat. A closed box on a Florida lift is heat. A charger that does not compensate, sitting on a flooded program in August, will gas a wet cell hard. Hydrogen has to leave the boat; that is a venting issue as well as a voltage issue.
Bring the charger photo
Brand, model, and the chemistry label or screen. Sarasota and Port Charlotte slip boats usually fail here, not at a mysterious cell. We match the program to the batteries that will actually be in the trays. A charger that finished on the wrong window will take a new pack with it, so the brick is part of the visit even when the case looks like the only failure.
Mixed banks on one brick
Flooded start plus AGM house on a single program will abuse one of them. The durable options are two chargers or a unit with per-bank profiles. We would rather say that on the quote than leave a new AGM on a flooded equalization schedule. If every battery on the boat is the same chemistry, one brain is fine — set it, then leave it alone.
Sources
- Battery University BU-403 — Charging Lead Acid
- Battery University BU-409b — Charging Lithium Iron Phosphate
If this is the job on your boat, see how we replace batteries at the boat. We come to you — Florida towns and counties.