FAQ
TL;DR: For an AGM that dropped to 8 V, a recovery attempt can use 0.8 A for "up to 14 hours"; if it stagnates, try gentle float or replace. [Elektroda, Anonymous, post #17257741]
Why it matters: This FAQ helps motorcycle owners revive or evaluate a deeply discharged AGM and decide when to stop trying.
Quick Facts
- Gentle desulfation: CC ≈50 mA for days, then discharge with a 12 V/1.2 W bulb and recharge; repeat cycles. [Elektroda, kortyleski, post #17258013]
- Alternative cycle: Discharge with a 10 W bulb to 9.5 V, then charge at 0.8 A until 15.6 V; repeat. [Elektroda, Anonymous, post #17257659]
- Time guidance: With 0.8 A “overclocked” charge, expect up to about 14 hours for a cycle. [Elektroda, Anonymous, post #17257741]
- Slow float approach: Hold at ~13.5 V for about a month to encourage sulfation reversal. [Elektroda, _jta_, post #17257523]
- Failure symptom: After charging to 13.6 V, dropping to ~10 V in hours suggests heavy sulfation. [Elektroda, porlock, post #17257305]
Can I revive an AGM battery that fell to 8 V over winter?
Yes, but it indicates sulfation. Connect it to about 13.5 V with low current and wait. Leave it connected for roughly a month. It may recover, though results vary. Consider the time and effort versus a replacement. Warranty terms might affect your decision. [Elektroda, jta, #17257523]
Why did my AGM show 13.6 V after charging, then fall to ~10 V?
That pattern points to sulfation after long discharge. The charger restored surface charge to 13.6 V, but plates stayed sulfated. The open-circuit voltage then settled near 10 V within hours. This behavior matches a battery that cannot hold energy. Try slow recovery first. [Elektroda, jta, #17257523]
What is a safe, gentle lab-supply recovery setup?
Do this:
- Set a lab PSU to constant current ~50 mA and connect for several days.
- Discharge using a small load (12 V, 1.2 W bulb).
- Recharge again at ~50 mA; repeat several cycles.
This slow cycling aims to dissolve sulfates without heating. [Elektroda, kortyleski, post #17258013]
How long will a 0.8 A, 15.6 V charge take on an 8 Ah AGM?
Using a lab supply, increase voltage to keep 0.8 A until the battery reaches 15.6 V. Expect up to about 14 hours per cycle. This is an effort estimate, not a guarantee of full recovery. "Up to 14 hours" was reported for this approach. [Elektroda, Anonymous, post #17257741]
How do I run the 10 W bulb plus 15.6 V method?
Discharge the battery with a 10 W bulb down to 9.5 V. Then charge with a lab supply in current limit at 0.8 A. Raise the voltage until the terminal reaches 15.6 V. Repeat the discharge/charge cycle and recheck performance. [Elektroda, Anonymous, post #17257659]
Is pushing 15.6 V safe for AGM desulfation?
Use caution with high voltage. "Too high voltage will result in gassing in some places, in other places it will leave sulfation." Uneven reactions can harm AGM cells. Prefer long, low-current charging for uniform chemistry. Monitor closely if you try higher voltages. [Elektroda, jta, #17257937]
How do I track whether desulfation is working?
Charge at a constant small current and time the rise from 12.0 V to 13.2 V. If that time increases over cycles, acceptance is improving. That signals gradual recovery. "The process of dissolving the 'insoluble' lead sulphate crystals takes a long time." [Elektroda, jta, #17258140]
How much capacity does 50 mA add over five days?
At 50 mA for 5 days, the math is 0.05 A × 120 h ≈ 6 Ah. This illustrates why the gentle method needs time on an 8 Ah battery. Expect slow gains rather than instant recovery, even with continuous charging. [Elektroda, Anonymous, post #17258050]
Will an automatic charger (e.g., Lidl) recover a deeply discharged AGM?
It can raise voltage to about 13.6 V, but a sulfated AGM may drop back to ~10 V within hours. That shows surface charge without restored capacity. Manual, controlled methods are usually required for recovery. The automatic cycle alone was insufficient here. [Elektroda, porlock, post #17257305]
When should I stop and replace the battery?
If repeated recovery attempts show no improvement, replace it. Forum advice in this case was clear: "Battery to be replaced." Weigh time and reliability risks against the cost of a new AGM unit. [Elektroda, Zielonka, post #17257313]
What rest voltage after charging signals the battery is still bad?
If it falls to roughly 10 V within a few hours after charging, it remains unserviceable. That behavior indicates heavy sulfation and lost capacity. Attempt one recovery run; otherwise plan a replacement to avoid failures. [Elektroda, porlock, post #17257305]
What about warranty—does storage-related sulfation get covered?
The thread raised this question but provided no answer. Review your actual warranty and storage clauses with the seller. Provide proof of purchase and any maintenance you performed when you ask. [Elektroda, porlock, post #17257597]
What discharge threshold should I use when testing with a bulb?
For the aggressive cycle, discharge with a 10 W bulb to about 9.5 V. Then charge at 0.8 A up to 15.6 V. Repeat as needed before testing the battery under load in the motorcycle. [Elektroda, Anonymous, post #17257659]
and he did not come to the conclusion that probably nothing of it, in other words, when I have to forgive myself, previously until 13.6 it took 2 days.
