Pages that sell reconditioning tend to skip this part. It is the part that saves you the most time and money, so it gets its own page here.
Replace it outright in these cases
The case is damaged
Cracks, splits, bulging sides or leaking electrolyte all mean the battery is scrap. A swollen case in particular indicates the battery has been overcharged or has overheated internally. Handle it carefully, keep it upright and take it to a recycling point.
A cell has shorted
If the battery will not climb past roughly 10.5 volts however long you charge it, or a hydrometer shows one cell far out of line with the other five, one cell has failed internally. This is a mechanical failure inside the battery, not sulfation, and no charging routine reverses it.
It fails a load test after a full charge
A battery that charges to a healthy resting voltage but collapses under load has lost the active material that actually delivers current. Voltage looks fine; capacity is gone. Reconditioning targets sulfation, not shed plate material.
It is simply old
Every lead-acid battery has a finite service life, and a typical car starting battery reaches the end of it after a handful of years, sooner in hot climates. Deep-cycle batteries are rated in charge cycles rather than years, and a golf cart pack that has been worked hard for several seasons is near the end regardless of how it tests today. On a battery that old, even a partly successful recovery tends to fade within weeks. Check the date code stamped on the case before investing effort.
It is lithium
Phone, laptop, power tool, e-bike, LiFePO₄ solar and EV batteries are lithium-ion. They do not sulfate, desulfation does nothing for them, and applying reconditioning voltages to them is a fire risk. Replacement is the only route. This is worth repeating because a great deal of material online blurs the two chemistries together.
Cases where recovery is possible but still not worth it
The battery is under warranty
Check the date code and your receipt first. Opening the battery, adding anything to the electrolyte or applying a non-approved charging routine will generally void the warranty. A free replacement beats an uncertain recovery every time.
Anything safety-critical depends on it
A recovered battery is, by definition, one whose reliability is uncertain. That is acceptable in a workshop, a garden machine or a spare bank. It is a poor choice for a vehicle you rely on in winter, a boat offshore, a medical device, an alarm system or emergency backup power. Use recovered batteries where failure is an inconvenience, not a hazard.
The economics do not work
Recovering a cheap car battery can easily cost more in electricity, equipment and hours than a new one, especially once you account for the core credit you get for returning the old one. Where the sums do favour recovery is on the expensive stuff — golf cart sets, forklift packs, large off-grid banks — because the replacement price is high enough that even a partial success is worth real money.
Worth trying
That leaves a fairly specific profile: a physically sound lead-acid battery, not too far into its service life, that sat discharged for a long period and now charges up but will not hold that charge. Even then, treat it as an attempt with an uncertain outcome rather than a repair with an expected result.
If you have not run the checks yet, the testing guide is where to start.
Service life figures here are general expectations, not guarantees. Real lifespan depends heavily on climate, charging habits, depth of discharge and how the battery was maintained. Follow your manufacturer's specifications where they differ.