Sitting is a discharge, even with no one on the boat
A battery left in the boat with a memory draw, a float switch, or a charger that lost power is sitting at a low state of charge. Battery University BU-802 describes sulfation from that condition. Kissimmee and Lakeland trailer pontoons that come off the water in May and go back in October are this pattern. The calendar is not the damage. The empty pack is.
Store charged, or take it off the boat
BU-403’s lead-acid advice is to store charged. A maintainer that actually floats at the right chemistry can stay connected. A cheap charger that never shuts up in a closed garage is heat on a sealed pack. The other honest option is to disconnect at the switch or remove the batteries to a bench maintainer. Leaving cables on and hoping is how October starts with a 10-volt surprise.
Flooded water before storage
Check electrolyte, then charge. Storing a flooded battery low on water as well as low on charge stacks two failures. Caps stay on after the charge. The box still needs a path for any residual gas. Do not bag a wet cell in a sealed tote with no vent.
Lithium storage is a SoC choice
LiFePO4 does not want to sit at 100 percent for six months, and it does not want to sit empty. Maker sheets usually pick a middle state of charge. The BMS may sleep. We follow that sheet rather than a lead-acid habit of “leave it on the tender all summer.”
Before you splash again
Charge, inspect terminals, and confirm the onboard charger still has a program. We can do that in the driveway. Off-season storage is not winterizing a boat that still fishes on Saturdays; it is the weeks or months the hull does not move.
Mice, heat, and a closed garage
A Florida garage in July is a hot box. A maintainer on a sealed AGM in that heat is still heat. Park the charger where air moves, or take the batteries to a cooler corner on a bench maintainer. Chewed cables are a spring surprise we would rather find in the photos you send before splash, not at the ramp.
Sources
- Battery University BU-403 — Charging Lead Acid
- Battery University BU-802 — What Causes Capacity Loss
If this is the job on your boat, see how we replace batteries at the boat. We come to you — Florida towns and counties.