Measuring Battery Voltage

[ccriders]

I have a two prong outlet in the companionway near the DC panel. If I measure the battery voltage at this point with a digital multimeter, how accurate of a reading can I expect?
John

[Maine Sail]

Originally Posted by ccriders

I have a two prong outlet in the companionway near the DC panel. If I measure the battery voltage at this point with a digital multimeter, how accurate of a reading can I expect?
John

What are you trying to determine with this reading?

[peikenberry]

The most accurate is at the battery

[mitiempo]

Very accurate for that point in the system. As posted the battery is the best place for voltage measurement and a voltmeter is usually wired direct to the battery. When nothing else is drawing power they should be close, the battery voltage a bit higher. If there is a large difference there is too much resistance somewhere from corrosion or an otherwise bad connection. Measuring voltage occasionally at different places on the boat can sometimes show problems you didn't know existed.

[rmeador]

If there is no load on this DC outlet, it should be a very accurate representation of the battery voltage. The voltmeter barely draws any current, so the voltage drop through the wires to the outlet will be negligible. If you're measuring it while it's under load, all bets are off.

[ccriders]

Thanks for your responses. I'm trying to keep track of battery status without replacing the current battery meter, which is worthless. The companionway outlet is very convenient and means I don't have to climb down into the cockpit locker, move a bunch of stuff open up the battery boxes and measure the batteries. There is probably six feet of 16ga wire (new) between the outlet and the terminal strip plus three feet of 16ga wire (new) between the switch panel and the terminal strip and then three feet of old wiring between the switch panel and the battery switch and six (?) feet of cable to the batteries. My guess that there has to be some voltage drop, but not significantly so. Based on the above comments a battery meter should be attached directly to the batteries, is that true? What gauge of wire should that be for say 10 -12 feet if wire?
Thanks for your help,
John

[mitiempo]

Yes, it is true a battery meter should be attached direct to the batteries.

A simple voltmeter will tell you voltage, but voltage is a lousy way to tell battery state. Ideally you can install a real battery monitor so you always know the exact state of charge of your battery bank. Like this: