On Nov 30, 1:57pm, Jon Mason Gougar Jr wrote:
> Apparently, a battery that is sitting, not hooked up to anything, will
> discharge at a rate of ten??? percent per month.
As Jon noted, the self-discharge rate is temperature dependent. Here is a
table I posted here some time ago that lists the self-discharge times for lead
acid batteries:
0 deg. C ( 32 deg. F) 7800 days
25 deg. C ( 77 deg. F) 1000 days
50 deg. C (122 deg. F) 180 days
70 deg. C (158 deg. F) 40 days
These are from the Gates battery book, and they indicate the time that it
takes for a lead-acid battery to fully discharge. As Jon also mentioned, a
battery will sulphate if left in a discharged state for any length of time.
Most battery manufacturers recommend recharging whenever the battery becomes
20% discharged to prevent sulphation. So, taking 20% of the above table
gives:
0 deg. C ( 32 deg. F) 1560 days
25 deg. C ( 77 deg. F) 200 days
50 deg. C (122 deg. F) 36 days
70 deg. C (158 deg. F) 8 days (!!)
Even discharged to this point, the freezing point of the dilute sulphuric acid
in the cells is < -60 deg. C (-76 deg. F!!), so you *don't* have to worry
about a car battery freezing, unless the battery has been run down totally
flat, so that the electrolyte has turned to water. (Once you did this, you
probably won't get the battery to hold a charge anyway, so it wouldn't matter
much if it did freeze!)
So, fully charge your battery in the fall and just disconnect the battery
leads. Don't bring your battery inside and set it next to the fireplace for
the winter! ;-)
Pat Vilbrandt Fluke Corporation Everett, Washington USA
pwv@tc.fluke.COM or: { uunet, uw-beaver, sun, microsoft }!fluke!pwv
|