Re: Battery Dying/Voltage

Jobst Vandrey (onlinenow@stlnet.com)
Mon, 12 Oct 1998 13:50:38 -0500


- - - - - - - - - - - - - - - - - - - - - - - - - - -
West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
- - - - - - - - - - - - - - - - - - - - - - - - - - -
>Here's a silly question. What voltage "should" a marine battery have when
fully charged?
>
>My battery is 3 or 4 years old (came with the boat from previous owner),
and when charged reads right at 12.0 volts. I've had it cranking out tunes
and the depthfinder over a weekend trip, without problem, and drop into the
11+ volt range before I got home to recharge it. It's a group 24 I believe.
>
>Is this consistent with what should happen, or should I look at replacing
it over the winter?

>From the Battery FAQ at www.windsun.com

On the table below, you have to be careful that you are not just measuring
the surface charge. To properly check the voltages, the battery should sit
at rest for a few hours, or you should put a small load on it, such as a
small automotive bulb, for a few minutes. The voltages below apply to ALL
Lead-Acid batteries, except gelled. For gel cells, subtract .2 volts. Note
that the voltages when actually charging will be quite different, so do not
use these numbers for a battery that is under charge.

Voltage at DOD
Here are some no load typical voltages vs depth of discharge.
(figured at 80% max discharge and 77 degrees F)
1% = 12.91 Volts.
10% = 12.8
20% = 12.66
30% = 12.52
40% = 12.38
50% = 12.22
60% = 12.06
70% = 11.90
80% = 11.70
90% = 11.42
100% = 10.50.

Regards

Jobst