...Or, do I just have a bum battery?

 

You'll need the exact model of your generac, and then, with the manuals for that model, it will explain how the charging of the battery happens. There's no alternator, but there is a charging module.

On my 22kw model, it doesn't charge the battery while running. Installation guide says run a separate 120v power line back out to the generac, and that is used to supply the charging module, which charges the battery (when the unit is not running; yes ... nobody can believe this is how it works).

Everyone hates this concept, wrt generacs; I was able to defeat it on my unit by putting a smart 12v battery charger on the battery, fed from an extension cord. Whenever it sensed that the battery wasn't optimal, it trickle-charged the battery.

You can charge the battery back up with any 12v battery charger; get a trickle-charger on it asap. If you think the battery is charged, but genny won't start, use a load tester on the battery.

Hope this helps ...

 

You'll need the exact model of your generac, and then, with the manuals for that model, it will explain how the charging of the battery happens. There's no alternator, but there is a charging module.

On my 22kw model, it doesn't charge the battery while running. Installation guide says run a separate 120v power line back out to the generac, and that is used to supply the charging module, which charges the battery (when the unit is not running; yes ... nobody can believe this is how it works).

Everyone hates this concept, wrt generacs, so I defeated it by putting a smart 12v battery charger on the battery, fed from an extension cord. Whenever it sensed that the battery wasn't optimal, it trickle-charged the battery.

You can charge the battery back up with any 12v battery charger; get a trickle-charger on it asap. If you think the battery is charged, but genny won't start, use a load tester on the battery.

Hope this helps ...

This is great info... thank you! Yeah - that sounds kinda funny, but I guess it makes sense.

 

You may want to check and see if there is any residual draw on that battery from the generator. If that is the case - a residual draw of even a few mA will drag batteries down over time and kill them completely - to where you can not even recharge them, much less try to pull starter current from them.

 

I did the opposite.... I disabled the generator's charging function (dumb bulk charger) and then connected an external smart battery maintainer.

It solves two things:
1. The generator is seldom used, even if I do a monthly exercise. That's not great for the battery.
2. The charging module on the generator is just a simple rectifier without a regulator. The charging voltage gets up to 17V and can potentially over-charge the battery on extended runs.

I know it doesn't solve your problem but this is just to say that you're going to be better off using an outboard smart charger.

 

and then connected an external smart battery maintainer.

I've done this on all my OPE, boats & backup cars now. I now have seven OptiMate 4 maintainers for the smaller batteries and an OptiMate 6 and several Schumachers for the larger batteries. I have not had to purchase a new battery since 2016.

 

I imagine there is an alternator or something similar to keep the battery charged.

If you have a multi meter you could do a charging system quick check. Put the leads on the battery posts and do a reading with the gen off and then while running.
2 example pics...