Charge It Up

Gray R. Riddick of Chocowinity, North Carolina, asks:"I know you have discussed using a multimeter to check a battery’s voltage. What does the reading mean? Will it tell me whether or not a battery should be replaced? My two house batteries, for example, read 12.82 and 12.36 volts."Nigel Calder replies: A specific voltage reading won’t tell
Author:
Updated:
Original:

Gray R. Riddick of Chocowinity, North Carolina, asks:

"I know you have discussed using a multimeter to check a battery’s voltage. What does the reading mean? Will it tell me whether or not a battery should be replaced? My two house batteries, for example, read 12.82 and 12.36 volts."

Nigel Calder replies:

A specific voltage reading won’t tell you much about a battery’s condition unless the battery has been rested for some hours; resting allows the voltage to stabilize. If the battery is in a stable state, there will be a correlation between voltage and its state of charge, but it will vary depending on the battery type—wet cell, gel cell, or absorbed glass mat (AGM.) In addition, wet-cell readings will also be affected by the concentration of electrolyte when the battery was made. To make any judgment about your two readings, I would have to know the battery type, whether the readings were taken after the batteries had been rested, and what the discharge rate was. Tracking a state of charge is much easier when you have a systems monitor installed; it can measure discharges and recharges and display the state of charge.

A voltage reading can be useful in checking the health of a charging system because you see how much voltage is reaching the batteries, rather than the voltage at the alternator or battery charger. Often there’s a voltage loss somewhere in the charging circuit that impairs performance—and ultimately battery life. A voltage reading across a battery’s posts when it is being charged should rise and then stabilize for a while at somewhere between 14.2 and 14.4 volts, depending on the type of battery and the system’s programmed parameters. Wet-cell batteries, for example, will typically be charged at 14.4 volts and AGMs at 14.1 or 14.2. As a battery comes up to full charge, voltage should drop to a float level, which can vary from a low of 13.2 volts (for many AGM batteries) to a high of 13.8 volts (for some wet-cell batteries). See my Boatowner’s Mechanical and Electrical Manual, 3rd edition, for more details.

Related

FB-BHM-1024

SAIL Black History Month Series: James Forten

James Forten was born on September 2, 1766 in Philadelphia to free Black parents Thomas and Margaret Forten. Forten attended a Quaker school as a young child, then went to work with his father who was a sailmaker. His father died when he was still young, and Forten worked ...read more

sailme-app_ SAIL

5 Ways Sail.me Helps You Monetize Your Boat

Ready to earn some extra funds by renting out your boat or yacht? Sail.me is an interactive service that allows you to monetize your boat in a secure, safe, and easy way. A user-friendly app and website will help you manage reservations, add-ons, and set customized routes to ...read more

VendeePromo

2020-21 Vendée Timeline

As a spectator event, France’s Vendée Globe never disappoints, and the 2020-21 edition of the quadrennial round-the-world race was no exception. From equipment failures to climactic rescues, heartbreaking abandonments and a breathtakingly close finish, this edition, which ...read more

valleytrunk3

BVI Chartering in the Pandemic

The week before I flew out to the British Virgin Islands for a bareboat charter, I was having a few second thoughts. The islands had broken out of their Covid-enforced tourism hiatus in December, but the conditions of entry seemed a little stringent: a negative Covid test within ...read more

01-LEAD-windfarm

Sailing Amid Offshore Wind Farms

Here in Europe, the general feeling about green energy from offshore wind turbines has moved on after an initial surge of general skepticism. Concerns raised over cost, threats to seabirds, wind interference and the rest have to some extent been answered, and it’s hard to argue ...read more

LunaRossaPrada

VIDEO: Luna Rossa Wins the Prada Cup

The show has gone on despite last week's Covid panic in Auckland, and the "underdog" Italians are victorious. After being bested by INEOS Team UK in the round robin section, they seemed to have an uphill battle ahead of them going into the finals. However, the Italians have been ...read more

FB-BHM-Cuffe-2048x

SAIL Black History Month Series: Paul Cuffe

Paul Cuffe was born on Cuttyhunk Island, Massachusetts, in 1759. His mother was a Native American woman named Ruth Moses, and his father was Kofi Slocum, a formerly enslaved man from the Ashanti Empire, located in modern-day Ghana. They had 10 children including Paul. His ...read more

Ryan-Finn

Point of SAIL: Ryan Finn on Solo-sailing a Proa Round Cape Horn

In this episode of Point of SAIL, Principal Editor Adam Cort talks with solo-sailor Ryan Finn, a veteran bluewater passagemaker looking to re-create the famed New York-to-San Francisco clipper aboard the 36ft proa, Jzerro. Although Finn was forced to abandon his first attempt ...read more