How to check if a battery is bad?

To check if a battery is bad, inspect for physical damage (swelling, leaks), test voltage with a multimeter (e.g., <12.4V for 12V lead-acid), and perform a load test. Lithium-ion batteries showing <10% capacity loss in 100 cycles or voltage drop >20% under load likely need replacement. Use battery analyzers for precise State of Health (SOH) readings below 80% indicating failure.

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What are the visual signs of a bad battery?

Swollen casings, electrolyte leakage, and corroded terminals indicate battery failure. Lithium cells bulge when gases form from thermal stress, while lead-acid batteries leak sulfuric acid crust (white/green powder). Check for warped seams on prismatic cells or cracked vents on cylindrical cells (e.g., 18650).

Beyond visible damage, inspect for thermal discoloration—blackened spots near terminals suggest overheating. Lead-acid batteries may show low electrolyte levels exposing plates. For lithium-ion, look for electrolyte odor (sweet, solvent-like) signaling membrane breakdown. Pro Tip: Use nitrile gloves when handling leaking batteries—sulfuric acid burns skin. Example: A swollen smartphone battery pushing against the screen confirms failure.

How accurate are voltage tests for diagnosing battery health?

Voltage tests provide surface-level insights but miss capacity degradation. A 12V lead-acid battery reading 12.6V (full) might drop to 10V under load if sulfated. Lithium-ion packs at 3.7V/cell could have 50% capacity left despite normal voltage.

Use a multimeter to measure open-circuit voltage (OCV) after 2-hour rest:

• Lead-acid: 12.6V (100%), 12.4V (75%), <12.0V (dead)
• Li-ion: 4.2V (100%), 3.7V (50%), <3.2V (damaged)

But what about internal resistance? Batteries with >200% increased resistance (vs specs) fail under load. Pro Tip: Combine voltage tests with impedance analyzers for reliable diagnostics. Example: A car battery showing 12.4V but struggling to start engines has high internal resistance.

When should you perform a load test?

Load tests reveal true capacity by applying 50% of CCA (lead-acid) or 1C discharge (Li-ion). Perform when voltage tests show partial charge but devices malfunction. Heavy machinery batteries need quarterly load testing—weak cells collapse under amperage spikes.

For lead-acid, use a carbon pile tester to apply ½ CCA for 15 seconds—voltage shouldn’t drop below 9.6V (12V battery). Lithium-ion requires specialized dischargers measuring capacity at 1C rate. Example: A 200Ah LiFePO4 battery discharging 100A for 2 hours (vs 2.5 hours when new) has 20% capacity loss.

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How do lithium-ion failure signs differ from lead-acid?

Lithium-ion fails via capacity fade and voltage plunge, while lead-acid suffers sulfation and acid stratification. Li-ion cells with >30% capacity loss often maintain voltage until sudden drops, whereas lead-acid shows gradual voltage decline.

Check lithium-ion cycle count vs specs—500+ cycles often degrade NMC cells. Lead-acid batteries fail faster if left discharged—48 hours at <12.2V causes permanent sulfation. Pro Tip: Use a hydrometer for lead-acid—specific gravity <1.225 indicates 50% discharge. Example: An AGM battery reading 1.20 SG needs equalization charging.

Can you recover a battery showing low voltage?

Lead-acid batteries below 12V may recover via desulfation pulses, but lithium-ion under 2.5V/cell risks copper shunts forming. Recovery depends on duration of under-voltage: Li-ion stored <2V for >1 week is unrecoverable.

For lead-acid, apply a 0.1C charge for 48 hours—if voltage rises above 12.4V, desulfate with 15V pulses. Lithium-ion BMS may block charging if cells dip below 2.5V. Pro Tip: Use a lab power supply to bypass BMS for recovery attempts, but monitor temperature closely. Example: A drone battery at 2.8V/cell might regain 80% capacity with slow charging.

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