Tech / Tech Articles

3 Ways to Bring a Deeply Discharged OPTIMA Battery Back from the Dead


OPTIMA Batteries are among the most-trusted and popular automotive batteries on the market. One of the great things about OPTIMA’s AGM-style batteries is their extremely low internal resistance. This allows very high amperage output enabling the battery to power your accessories longer and deeper than a traditional battery while discharging it at the same time.

But even the best batteries can fail, especially when starting batteries are used for deep-cycling applications (learn more about choosing a battery here and here). In many cases, though, OPTIMA batteries that are pronounced “dead” are actually just deeply discharged. According to OPTIMA, these AGM-style batteries can be resuscitated and saved using three different methods. Before you send your battery to the car parts graveyard, give one of these solutions a try:

1. Use a AGM-Specific Charger

An AGM battery can stump car guys because it doesn’t work like a traditional flooded lead-acid battery. They may hook a seemingly bad OPTIMA battery to the old tried-and-true battery charger and get no signs of life.

Here’s the problem.

Most battery chargers have built-in safety features which prevent them from recharging deeply discharged batteries. If a traditional battery is at 10.5 volts or less, an analog charger will remain off because the battery is seen a defective. The charger will remain off because charging a “bad” battery could create an unsafe scenario. The AGM battery may be just fine, but has slipped below the minimum voltage threshold of the charger to turn on.

That’s why it’s important to purchase a modern, AGM-specific charger for your AGM-style battery.

AGM-specific battery chargers have special settings and desulfation steps that help recondition and recover deeply discharged AGM batteries. These are becoming more common, and they work well for all lead-acid batteries, too. They have the additional capability of doubling as a battery maintainer for batteries in storage. OPTIMA offers a Digital 1200 12V Performance Battery Charger and maintainer that enhances the performance of OPTIMA and other AGM batteries, recovers deeply discharged batteries, and extends battery life.

This is the preferred method of charging a deeply discharged battery.

2. Try the DIY Solution

Want to stick to the charger already in your garage?

OPTIMA offers an alternative that tricks your traditional charger into charging the deeply discharged AGM battery. According to OPTIMA, here’s what you need:

  • Battery charger (under 15 amps)
  • Jumper cables
  • A good battery, preferably above 12.2 volts. (It can be an AGM or flooded battery.)
  • The seemingly dead, deeply discharged AGM battery
  • A voltage meter
  • A watch or timer

Start by hooking up the good battery and deeply discharged AGM battery in parallel — positive to positive and negative to negative. Next, hook up the good battery to the charger and turn on the charger. The charger will “see” the voltage of the good battery (hooked up in parallel) and start providing a charge. After the batteries have been charging for an hour, check to see if the AGM battery is slightly warm or hot to the touch. Batteries naturally become warm during charging, but excessive heat may be an indication that there really is something wrong with the battery.

IMPORTANT: Discontinue charging immediately if the battery is hot to the touch or if you hear the battery “gassing” — a hissing sound coming from the safety valves.

With your voltage meter, check back often to see if the AGM battery has charged to 10.5 volts or above. This generally takes less than two hours with a 10-amp charger. Once it reaches the 10.5-volt threshold, disconnect the charger from the wall outlet and remove the good battery from the charger. Now, connect only the deeply discharged AGM battery to the charger. Turn on the charger and continue until the AGM battery reaches a full charge, or until the automatic charger completes the charge process.

3. Get Professional Help

You can always take your battery to a professional battery specialist who knows AGM technology. Most auto parts stores use conductance testers that don’t provide correct readings, so we’d recommend a battery specialist like Interstate Batteries or other independent battery distributors. Most of these places are willing to provide “charge and check” procedures free or for a small fee and can determine if your battery is recoverable.


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  1. Mastermech48 says:

    Good to Know

  2. Have a small hump on top of my optima is it safe to try to charge it its dead

    • Hey Fred, are you saying the battery has developed a bump, like a small lump on the top of the battery? If so, that’s a pretty good sign that battery needs to be replaced. The hump may have been caused by built-up gas trying to exit the battery’s housing as a result from overheating. (Which, in turn, can be caused by loss of electrolyte, freezing temperatures, a bad regulator, shorted cells, etc.) DO NOT attempt to charge it.
      Pull the battery out and take it to your nearest battery recycling facility–most shops that will sell you a new car battery will typically take your old one for you.

  3. I use 2 gel batterys in my wheelchair. C5 size 12 v in series. 95ah
    Did not use for long period and batterys completly discharged. Only show millivolt
    Is possible to revive?

    • Long periods of a battery in or below 10.5 volts can cause sulfates to grow and then inhibit charging. After a certain point the battery becomes so sulfates that it can not be recovered. You can Try a battery pro as stated in the article.

  4. H. J. Moleman says:

    Here is something I have been doing with my yellow top optima battery. I stay away from normal battery chargers. It may not be the proper method to recharge, I am aware of this. I use a RadioShack 3-12V DC adapter on 12V setting. It puts out 12.38V @3.5 amps.
    Any 12DC adapter works, the more amps, the quicker the charge. Takes about a day to charge enough to crank the engine. Don’t have to drag or roll any lunker battery charger either, just roll out an extension cord, hook up the polarity correctly on the adapter and tomorrow we’re good to go.

    I purchased my optima battery in 2008. 115 degree summers/20 degree winters. Still working wonderfully. It has been worth every penny.

    • This is not a bad way to charge a battery, my most concern would be over charging the battery and gassing, loss of water. If you use a volt meter and disconnect the battery when charged you will be fine , as all your battery. Some cheap battery maintainers use a “wall wart” style plug that’s simply see 14v and cuts off or floats around this number..
      *Always use PPE suffering acid can/will blind you*

  5. Stephen Hobrecht says:

    I have a 6V Optima that is almost 7 years old and has been on a float charger all of it’s life. The old car sit’s 99.99% of the time so I expected the battery to live for another couple of years but have been unable to bring it back to useful life. I had been float charging it at around 6.5V but that may not have been high enough.

  6. Great review, really helps us trying to decipher this ‘new’ world of LiFePO4 batteries for our leisure needs. I really like the price of the RUiXU, I know it has some limitations but these are not going to affect everyone. Thanks, Will!

  7. Jim Dickinson says:

    My 14 month old 12 volt Optima (yelleow top) battery reads only 6.6V. It sat, unused, in my Prius for a month. I put it an my older charger (my 2 smart chargers read a fault) to no avail.

    • Robert Haynam says:

      Similar circumstance with battery reading 6 volts and charger showing green light, fully charged? I again attempted to charge again in AGM mode with another battery jumped to the Yellow Top, the charger then proceeded showing 12 volts and 24%. It has now been over 24 hours and the battery is back to 82%. This battery is only 4 months old but sat unused for a number of months. I’m hopeful it comes back to 100% but that remains to be seen??

  8. Daniel Ryan says:

    My car battery was completely dead from letting it sit all winter, I jumped it, got it started and it ran but didn’t hold a good enough charge. I then put it on the charger for my 4 wheeler overnight and it’s worked fine since. It still works good, and pushes my subwoofers just fine.

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