Marine Battery and Electrical Log

What this sheet is for

Track battery voltages as a series rather than a single reading, so a bank that is dying is obvious well before it strands you.

Who it is for

Boat owners with a domestic battery bank, shore power or solar, and anyone chasing an intermittent electrical fault afloat.

How to use it

1. Record the bank once — chemistry, capacity and the date each battery went in.
2. Take resting voltage after the bank has been off charge for a while, or it means nothing.
3. Record voltage under load as well as at rest; that is where a tired battery shows.
4. Log anode wear at each lift-out, with where each anode was.

What is on the sheet

The layout is fixed at a size that fits both A4 and US Letter, so the A4 and Letter files are visually identical and print at full size on either. Rows are set at a height that an adult can actually write a date and a few words into with a pen — most printable tables are built in a word processor and never tested with one.

Questions

Why record a resting voltage and a voltage under load?

A resting voltage tells you roughly how full a battery is. A voltage under load tells you whether it can still deliver current, which is the thing that actually fails. A battery can read fine at rest and collapse the moment the windlass runs.

Does the charger need changing if I fit different batteries?

Charging profiles differ between chemistries, and fitting lithium where flooded lead-acid was is not simply a swap — the charger, the alternator arrangement and the protection may all need attention. Take the settings from the battery manufacturer and record what you set, which is what the log is for.