Cummins/Onan — Battery Specific Gravity Check
Maintenance · Batteries
From a Cummins/Onan operator's manual — check it applies to your exact model before use.
Applies to: Cummins/Onan DFBF, Cummins/Onan DFCB, Cummins/Onan DFCC, Cummins/Onan DFCE, Cummins/Onan NT855 engine, Cummins/Onan NTA855 engine
Before you start
- Electrolyte is a dilute sulfuric acid that is harmful to the skin and eyes. Wear goggles and protective rubber gloves and apron when servicing batteries.
Procedure
- Use a battery hydrometer to check the specific gravity of the electrolyte in each battery cell.
- Hold the hydrometer vertical and take the reading.
- Correct the reading by adding four gravity points (0.004) for every ten degrees the electrolyte temperature is above 80°F (27°C).
- A fully charged battery will have a corrected specific gravity of 1.260. Charge the battery if the reading is below 1.215.
Tools required
- Battery hydrometer Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Fully charged corrected specific gravity 1.260
- Charge if reading below 1.215
- Add 0.004 for every 10°F above 80°F (27°C)
Full service-parts list: Cummins/Onan DFBF →, Cummins/Onan DFCC →, Cummins/Onan DFCE →
Source: Cummins/Onan operator's 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.