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ErrorLib — Industrial Fault Code Library

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28

Deeply Discharged Battery (Safety Charge)

Fronius · Perfect Charging

What does 28 mean?

The connected battery is heavily discharged, meaning its voltage is significantly below its normal operating range. The charger has initiated a special 'safety charge' or 'recovery charge' phase at a very low current to safely bring the battery voltage up to a level where normal charging can begin. This is a protective measure to prevent damage to deeply discharged batteries.

Common Causes

  • Battery has been left in a discharged state for an extended period
  • High parasitic loads have completely drained the battery
  • Faulty battery that cannot retain charge, leading to deep discharge

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Monitor the battery voltage to ensure it slowly rises during the safety charge phase

  2. 2

    Do not interrupt the safety charge process; allow the charger to complete this phase automatically

  3. 3

    If the battery voltage does not rise after a prolonged safety charge, the battery may be unrecoverable or faulty

Browse all codes in this manual (61)
Verified technical data. Last updated: April 2026

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Source: Fronius Perfect Charging
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