Cummins/Onan 12.5 RDJC / 15.0 RDJC — Battery Cleaning and Specific Gravity Check
Maintenance
For the Cummins/Onan 12.5 RDJC / 15.0 RDJC, from the Cummins/Onan operator's manual.
Applies to: Cummins/Onan 12.5 RDJC, Cummins/Onan 15.0 RDJC, Cummins/Onan RDJC
Before you start
- Do not smoke or allow any source of ignition while servicing batteries
- Always remove the negative (-) cable first, and reconnect it last to prevent arcing
Procedure
- Disconnect the negative ground strap from the battery before working on any part of the electrical system or engine.
- Wipe the batteries clean with a damp cloth whenever dirt appears excessive.
- If corrosion is present, remove battery cables and wash terminals with an ammonia solution or a solution of 1/4 pound baking soda in 1 quart of water.
- Flush the outside of the battery and surrounding areas with clean water.
- Coat the terminals with a light application of petroleum jelly or non-conductive grease.
- Use a battery hydrometer to check the specific gravity of the electrolyte in each cell; hold the hydrometer vertical.
- Correct the reading by adding four gravity points (0.004) for every ten degrees the electrolyte temperature is above 80°F (27°C).
Tools required
- Battery hydrometer Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- A fully charged battery has a corrected specific gravity of 1.260
- Charge the battery if the reading is below 1.215
- Check electrolyte level at least every 200 hours of operation
Full service-parts list: Cummins/Onan RDJC →
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.