Cummins/Onan — Checking Battery Charge Condition
Maintenance · Starting battery
From a Cummins/Onan service manual covering: 4BT3.9, 4BT3.9-GC1, 4BT3.9-GC2, 6BT5.9, 6BT5.9-GC1, 6BT5.9-GC2, 6CT8.3, 6CT8.3-GS/GC1, 6CTA8.3, 6CTA8.3-GS/GC1, 6CTA8.3-GS/GC2. Check it applies to your exact model before use.
Applies to: Cummins/Onan 4BT3.9, Cummins/Onan 6BT5.9, Cummins/Onan 6CTA8.3, Cummins/Onan 4BT3.9 engine, Cummins/Onan 6BT5.9 engine, Cummins/Onan 6CT8.3 engine, Cummins/Onan 6CTA8.3 engine
Before you start
- Ignition of explosive battery gases can cause severe personal injury; do not smoke while servicing batteries. Wear protective apron and goggles.
Procedure
- Check that connections are clean and tight; apply light coating of non-conductive grease.
- Check charge condition of starting batteries with a hydrometer.
- Keep electrolyte at proper level above plates by adding distilled water.
- Check specific gravity and re-charge if below 1.260.
Tools required
- Hydrometer Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Re-charge if specific gravity below 1.260
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.