Criteria for Judging When to Replace Batteries of Scissor Lifts

Two main battery types are used on most scissor lifts: deep-cycle lead-acid batteries (24V system, configured as four 6V units or two 12V units) and lithium iron phosphate (LiFePO4) batteries. The judging logic applies to both types, with only numerical thresholds differing.

I. Abnormal Operating Performance of Equipment (Most Intuitive On-Site Judgment)

If two or more of the following symptoms occur, the batteries are generally aged and require replacement:

1. Sharply reduced service runtime
   After a full charge, the actual operating time drops to 50% or less of that of new matching batteries. Repeated recharging mid-shift becomes mandatory to complete regular work tasks.
2. Weak lifting and driving power
   The lifting speed slows noticeably, and the motor runs sluggishly with dull noise. The machine loses significant speed when climbing slopes or lifting full loads; in severe cases, the platform automatically drifts downward halfway up. The battery level indicator plummets rapidly.
3. Severe voltage drop under load with premature power cut-off
   The static full-charge voltage reads normally, yet the overall pack voltage plunges sharply the moment lifting or driving loads are applied. The battery gauge drops abruptly from full to low-power shutdown without gradual warning.
4. Abnormal charging behavior

• Greatly shortened charging duration: The charger switches to the green fully-charged indicator after only 3–4 hours, compared to the original 8-hour charging cycle, while the actual stored capacity remains insufficient.
• The charger frequently trips into protection mode and cycles on and off intermittently.
• Severe self-discharge occurs after overnight parking; the machine triggers a low-battery alarm the next morning upon startup.

1. Frequent low-voltage protective shutdowns
   The machine locks up and cuts power unexpectedly during site operations and can only be reset after recharging. After ruling out wiring and controller faults, this indicates excessive internal resistance and severe capacity degradation of the batteries.

II. Physical Appearance Damage (Immediate Decommissioning & Replacement Required for Any Single Symptom; Severe Safety Hazards Exist)

1. Swollen or deformed battery casing
   Lead-acid batteries bloat from overcharging or aging gas buildup; lithium batteries expand due to internal thermal swelling. Bulged housings fail to fit neatly into the battery compartment. Continued use is strictly prohibited due to risks of electrolyte leakage and fire.
2. Electrolyte leakage, acid seepage, or cracked casings
   Flooded lead-acid batteries spill electrolyte, leaving white corrosive residue on housings. Sealed maintenance-free batteries leak from gaps, corroding wiring harnesses and the machine frame. Any cracked casing renders the battery irreparable.
3. Heavily oxidized and hot terminal posts
   Terminals are covered in thick white or green corrosion deposits that regrow rapidly after grinding. Terminal lugs heat up noticeably during lifting operations, a clear sign of excessive internal resistance.
4. Abnormally fast electrolyte consumption for flooded lead-acid batteries
   Under normal conditions, only minimal distilled water top-ups are needed weekly. If large volumes of distilled water must be added every 2–3 days, electrode plates are severely corroded and the battery cannot be restored.
5. Excessive heat and peculiar odors during charging
   Battery temperature exceeds 50°C while charging, accompanied by sour acid fumes or burnt plastic odors, and boiling electrolyte. Severe plate sulfation has occurred, making repair impossible.

III. Professional Testing with Multimeters / Load Testers (Accurate Verification Mandatory for Maintenance)

1. Static full-charge voltage standards (test after resting for at least 4 hours)

• 24V lead-acid battery pack: Healthy voltage range 25.2–25.6V; single 6V cell 6.3–6.4V.
  Replacement is required for poor cell consistency if any single cell measures below 6.0V, or the voltage difference between individual cells exceeds 0.3V. Full pack replacement is recommended.
• 24V LiFePO4 battery pack: Full-charge voltage around 26.4V. Severe degradation is confirmed when the voltage difference between individual cells exceeds 0.2V.

2. Voltage drop test under load (Core Judging Criterion)

With the battery fully charged, lift the platform to maximum height under full load and monitor voltage fluctuation:

• Healthy batteries: Voltage drop ≤1.5V
• Worn, end-of-life batteries: Voltage drop ＞3V, often triggering low-voltage protective shutdown instantly.

3. Capacity test thresholds (Industry Standard Replacement Benchmarks)

Actual capacity measured via discharge tester:

• Measured capacity ＜70% of rated capacity: Mandatory replacement, as sudden mid-air shutdown poses critical safety risks during elevated work.
• 70%–80% rated capacity: Temporary limited use permitted; prepare replacement batteries in advance.
• ＞80% rated capacity: Minor degradation only; continued use is acceptable after cell balancing maintenance.

4. Abnormal internal resistance

If the internal resistance of one cell in the pack is more than double that of others, the cell suffers internal sulfation or plate shedding and cannot be repaired.

IV. Service Life & Cycle Count Reference (General Replacement Timelines)

Deep-cycle lead-acid batteries (Most common on construction sites)

• Heavy-duty operation (rental fleets, daily full-load site use): Reach replacement cycle after 1.5–2.5 years.
• Light indoor use with proper maintenance: Maximum service life 3–4 years.
• Replace when exceeding 400 charge-discharge cycles, after which capacity declines rapidly.

Lithium iron phosphate batteries

With proper maintenance and standardized charge-discharge cycles: Service life 5–8 years. Conduct annual capacity testing after 6 years; replace immediately if State of Health (SOH) drops below 70%.

V. Distinguish Battery Failures from Other Electrical Faults (Avoid Unnecessary Battery Replacement)

Rule out the following issues before confirming battery failure:

1. Damaged chargers or mismatched charging parameters
2. Loose battery terminals, damaged wiring harnesses, or poor fuse connections
3. Faulty drive or lift motors and controllers
4. Malfunctioning voltage sensors on the instrument panel
6. Simple troubleshooting method: Install a confirmed functional battery from an identical machine. If the equipment recovers full power, the original battery pack is defective.