Battery drained completely--does this hurt the battery?
 

I recently purchased an Oddessey 925 battery (within the past year). Does it harm the battery to let it lose its charge completely? My car has not been started in the past 3 months and now when I tried to start it, the battery is completely drained. My car has sat in the garage for the past 3 months unstarted. Thanks

Yes- it will shorten tha battery's life.

I use a $30 battery maintainer to keep the battery fully charged.

Hey, from a former Husker, I had the same problem. I solved my drain with a battery cut off switch. When I park it, I just turn the green knob, and wha-la, no juice. I've got a batter tender, but I had problems with them in the past and I dont really trust them when Im not at home. You can buy the cut off switch through most catalogs.

Aftermarket Stereo amplifiers tend to drain batteries. Mine was drawing .5Amp with the ignition switch off. Got rid of the amp (used the small amp in the radio) no more problems.

From the odyssey site....

German DIN standard test for overdischarge recovery
In this test, a charged PC 925 was discharged over 20 hours (0.05C10 rate) to 10.20V. After
the discharge5 was complete, a 5W resistor was placed across the battery terminals and it was set
aside for 28 days.
At the end of 28 days’ of storage, the battery was charged at 13.5V for only 48 hours. Another
0.05C10 discharge yielded 97% of rated capacity, indicating that a low rate 48-hour charge after such
as deep discharge was not sufficient; however, the test is designed to show whether the battery can
be recovered from extremely deep discharges using only a standby float charger. A standard
automotive charger at 14.4V would have allowed the battery to recover greater than 97% of its
capacity.
The results of this test conclusively prove that ODYSSEY® batteries can recover from very
abusive storage conditions. This conclusion is further reinforced by the following test that is even
harsher than the DIN standard test due to the fact that the battery was stored in a discharged state
at a temperature of 50°C or 112°F.

Even a well-made battery will have decreased service life if repeatedly cycled (discharge, charge, discharge, charge, etc.).

The best solution is to keep it fully charged.

Sherwood

The Bad News:

Battery discharge converts the lead surface of the internal lead plates to lead sulfate (sulfation). If the battery is immediately recharged (as is immediately after you start your car) most of the lead sulfate is converted back to elemental lead. A battery that is fully discharged, or remains at a low charge for a long period of time, forms lead sulfate crystals on the surface of the plates that are not removed by normal charging. The area covered by lead sulfate crystals becomes unavailable for electricity generation, and the total capacity of the battery is reduced by that percentage of surface area loss.

The Good News:

Automotive batteries have a significant excess capacity so they can handle the lights being left on all day (full discharge), very cold starts, etc. One or two accidental discharges of your battery will normally not reduce its capacity to a level you will notice, but know that each time it is fully discharged, the electricity generating capacity becomes reduced by a fixed amount.

What you should do:

If you accidentally fully discharge your battery, you should restore its charge at the earliest opportunity. Do not rely upon your alternator to do this, but use a battery charger. If your battery has been dead and under a steady drain for 3 months, it's probably toast. If you do not drive your car at least once a week, then either put a smart trickle charger on the batter in the car, or remove the battery from the car and use the smart trickle charger to charge it up once a month or so, as sulfation occurs in a battery on the shelf once the charge drops to 80% or so of optimal.

Is this the kind that gas stations have? Is there a home version?

I use the Battery Tender Jr. and it works fine overall, but it's not intended to charge a battery from zero.

I use a charger I bought at auto zone for about $40. It has two charge levels, 2 and 10 amp. 2 amp will maintain a battery with about six hours a week of charging, and the 10 amp setting has brought several batteries back from a full discharge in 3-5 hours. Alas, it is not one of the high tech ones that shut off automatically, but it has a guage that gives the charge state of the battery so I know when it is fully charged.

I think all automotive chargers charge at 14V so they do not damage the battery, the difference is in the amperage they deliver. Auto repair shops sometimes have high amperage pulse chargers. Some people believe that short, high amperage pulses, with resting periods to allow the battery to cool down, reduces sulfation in the battery, but I do not know if that is true or not.

Shops also have equipment to perform diagnostics on the battery after charging, so if you can be sure that the battery is not a goner after charging.

SUPER information guys thanks. I put a charger on it overnight and it showed 100% charged in the morning. I won't let it go completely drained again. Probably will pick a charge or remove that battery if its going to sit for an extended period.

Get the kill switch. Solves a LOT of problems:

Less chance of a discharged battery
Reduced incidence of theft
Longer battery life/less chance it'll crap out on you

normal automotive batteries service life is shortened by complete discharges

but

marine deep cycle batteries are designed for exactly that sort of thing