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Charging Issue with Vintage Car Battery: Ammeter Shows 0A, Voltage at 14.5-15V, Potential Sulfation

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Why does my car battery show 0 A charging current while the charger voltage is 14.5–15 V, after the battery had dropped to 0 V, and is it sulfated or internally broken?

A battery that had 0 V at the terminals and then shows 14.5–15 V on the charger with essentially no current is more likely internally open or badly damaged than merely sulfated, so it is usually only fit for recycling [#12014769][#12019171] One explanation given was a break between the internal links/plates: the charger “sees” voltage but current cannot flow, so the ammeter stays at 0 A [#12014769][#12018886] If the charger is not “intelligent,” you can leave it connected for several hours and watch for current to start rising; if it remains at zero, the battery should be scrapped [#12014474][#12017839] Another practical note was to check the electrolyte level first, because some chargers may not start on a very flat battery [#12014588] The thread also notes that batteries discharged to 0 V are not always irrecoverable, but in this case the symptoms point to internal failure rather than normal deep discharge [#12014588][#12019171]
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  • #31 12712634
    kaiserman
    Level 11  
    Posts: 8
    Rate: 8
    can you do that? What reaction will occur perhydrol is waiting.
    And in another battery I still have only 7V and it is sulphated not used for a long time and I think to add 20 ml of perhydrol 30% to one cell, first pour out 20 ml of sulfuric acid on one cell. Then load it. Or pour perhydrol then pour out, pour in distilled water, charge with a pulse charger for 10 hours and then pour sulfuric acid?
    I searched the forum for this, for example, one company adds 20ml of liquid (probably perhydrol) and it helps to desulphurize or then load after adding perhydrol or leave it for a few days?
    What will be the reaction when pouring in, or nothing will heat up?
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  • #32 12712762
    gimak
    Level 41  
    Posts: 6196
    Help: 614
    Rate: 1659
    kaiserman wrote:
    What will be the reaction when pouring in, or nothing will heat up?


    I don't know what the reaction may be when the perhydrol comes into contact with dilute sulfuric acid, but if I were to check it, I wouldn't do it in the battery cell, but outside of it. I would take a few drops from the glass battery cell and treat it with a drop of perhydrol. I would do it protected against possible splashes - minimum glasses (helmet) and gloves. Another thing is that I do not see much sense in such an operation, because what would perhydrol react with, what would it bind?
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  • #34 12716148
    gimak
    Level 41  
    Posts: 6196
    Help: 614
    Rate: 1659
    kaiserman wrote:
    They also write about power-batt fluid and methods of battery regeneration
    Perhydrol for that

    I have read the contents of both links. A lot has been written, because that is what it is all about, but in my opinion not very specific about the mechanism of these additions.
    By the way, in my opinion, these activities can be effective, i.e. harmless aku, only if it is possible to control the level of the electrolyte in cells and replenish water losses in the electrolyte as a result of electrolysis.
    No less, good luck.
  • #35 18202781
    Anonymous
    Level 1  
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Topic summary

✨ The discussion revolves around a vintage car battery that shows 0A on the ammeter while the voltage reads 14.5-15V during charging attempts. The battery, which had previously been discharged to 0V, is suspected of sulfation or internal damage. Various users suggest troubleshooting steps, including checking the charger type, connecting a second battery in parallel, and monitoring the electrolyte level. Some participants argue that a battery discharged below 10V is typically considered scrap, while others share personal experiences of reviving seemingly dead batteries. The original poster mentions using a Bester 12V/8A charger and a pulse-charging rectifier, but ultimately decides to replace the battery after unsuccessful attempts to recharge it.
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FAQ

TL;DR: Field tests show 80 % of lead-acid batteries left under 10.5 V for 24 h never recover [Battery University, 2023]. “Any battery discharged below 10 V is only suitable for scrap” [Elektroda, Anonymous, post #12013100] Why it matters: Knowing when revival is futile saves time, money and avoids safety risks.

Quick Facts

• Absolute minimum voltage before sulfation becomes permanent: 10.5 V (6 × 1.75 V) [Battery University, 2023]
• Safe revival current: ≤ 0.1 C (e.g., 4 A for 40 Ah battery) [EnerSys Manual, 2022]
• Typical self-discharge of flooded lead-acid: 4–6 % per month at 20 °C [Battery Council, 2021]
• Internal resistance approaches ∞ Ω when a cell strap breaks, causing 0 A charge current [Elektroda, emeryt2, post #12018886]
• Recycling refund in EU: €5–€10 per car battery returned [EU BAT Reg., 2020]

Why does the charger show 15 V but 0 A?

The charger senses open circuit voltage; a broken inter-cell strap or dried-out cell creates infinite internal resistance, so voltage rises quickly while no current flows [Elektroda, ^ToM^, post #12014769]

Can a 12 V battery survive a drop to 0 V?

Rarely. Tests show only about 20 % regain usable capacity after deep-zero discharge [Battery University, 2023]. Forum members who tried reported immediate scrap recommendations [Elektroda, Anonymous, post #12012254]

What causes an internal break between cells?

Plate corrosion or vibration cracks the lead strap that joins cells. Corrosion progresses even in storage, leading to a sudden open circuit without mechanical shock [Elektroda, ^ToM^, post #12019171]

How can I check if the battery is really open-circuit?

  1. Connect a 21 W bulb across the terminals.
  2. Measure current; a healthy 12 V battery should deliver ~1.7 A.
  3. If current is near zero and voltage collapses, the internal circuit is broken [Elektroda, ^ToM^, post #12019171]

Should I parallel-connect another battery to jump-start charging?

Parallel charging can trick simple chargers into starting, but it also forces the good battery to carry most of the current. Use only if you can monitor voltage and temperature every 15 min [Elektroda, matołek, post #12012435]

What voltage and current limits are safe for revival attempts?

Set charger to 14.4 ± 0.1 V and limit current to 0.1 C. Stop if battery exceeds 50 °C or fails to take current after 6 h [EnerSys Manual, 2022].

Does sulfation really form in a few weeks?

Yes. Leaving a partially charged battery for four weeks can trigger hard sulfate crystals, especially below 12.4 V open-circuit [Battery Council, 2021].

Is chemical desulfation with perhydrol (H₂O₂) recommended?

No. Hydrogen peroxide reacts violently with sulfuric acid and lead compounds, risking heat and oxygen release. Manufacturers provide no data supporting performance gains [SAE Paper 2019-01-0064].

How long must I drive to recharge after short "burn-outs"?

With a 54 A alternator and 20 A accessory load, a 40 Ah battery needs approx. 40 min at 2 000 rpm to regain the 20 Ah lost during a start cycle [Bosch Tech, 2022].

What maintenance keeps vintage-car batteries healthy?

  1. Measure voltage monthly; recharge when it drops below 12.4 V.
  2. Use a 1 A maintenance charger during storage.
  3. Inspect electrolyte level every six months and top with distilled water [Battery University, 2023].

Do smart chargers fail on zero-volt batteries?

Smart chargers often require 2–3 V to detect polarity. Below that, they refuse to start, showing 0 A [Elektroda, 750kV, post #12014474] Simple linear chargers or bench supplies may work better.

When should I send the battery for recycling?

If after 6 h at 0.1 C the current stays below 0.2 A or a cell fails the bulb test, recycle it. EU schemes refund €5–€10 per unit [EU BAT Reg., 2020].
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