8.5 kohler generator battery dies often - Kohler 12 kW Emergency Power System - 12RES-L

That is an engine running issue, not a battery issue. :>D The first thing to check would be fuel supply. Can you start up manually and keep it running. If you can, it is the contactor that senses your loss of mains power and switches the generator on. It is not maintaining the connection, or is is misdiagnosing the power from the generator as power from the mains.

Jack' Small Engines, or the maker.

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You didn't specifiy which model Kohler generator ???

If it won't start in manual, you have a short and/or a bad control board. Make sure battery polarity is correct, did you disconnect battery charger before removing old battery? If not charger can push DC volts over 20V and can damage control board.

The battery charger is defective, as you can start it by jumping it off means it is just a low battery. without it running measure battery voltage, it should be around 12V then plug the charger back in, it should climb to around 13.8B with a good battery. If not have the float charger checked.

Check the oil pressure switch, and oil level first. Then check rotor brushes and rotor slip rings may need polishing. If the problem is still there check stator and rotor windings

Is there a fault?? All UL listed generators including Kohler are required to lockout on a fault on shut down. This really sounds like a problem with your 2-wire auto start connection between your automatic transfer switch and genset. RDT model automatic transfer switch it is the 2 middle wires on the green connector and terminals 3&4 in the generator. close to run and open to shut down. Any open at any time will cause the unit to shut down. The 12 will shut down instantly upon an open because your 5 minute cool down is built into the transfer switch.

The rpm sensing in the control module is missing or bad.
Answer these questions for more details:

1. Does your generator output normal voltage?
2. Is the starter turning after the Gen is running?
3. Is the charging of the battery connected?

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