Is it my starter motor?

Completely impractical and actually near impossible on a 308. The solenoid is with the starter at the front bottom of the engine, accessible only from underneath.

As for chargers, you should completely charge a new battery before installation. If the battery needs major charging, a trickle charger/tender isn't up to tha task. Go to Sears and get a real charger. A tender is just for maintaining a good battery.

I think you probably have an alternator/regulator issue which has discharged the battery.

Get the voltages Milton suggests.

Birdman

 

I'm still putting my money on battery cable connections. Scrape inside of connectors b4 attaching to battery. Verify negative cable attachment at frame clean & tight.
Bill

 

The latest info sounds better as far as battery and alternator state is concerned, so it was probably just a new battery that had a low charge. When you first said the battery stayed at 11.6V after charging, I assumed you were talking about a typical 2A/10A charger and that would indicate a bad battery. However, if it was one of those fractional amp trickle chargers, then that wouldn't be much charging at all.

When you measure your battery under charge, you should see between 13-14V, that is the extra voltage needed to put a charge on the battery. On its own with no charging voltage, a fresh battery should settle around 12.6V. Anything below 12V indicates the battery is almost completely discharged or is faulty, such as a bad cell. An automotive battery that is deep discharged can also sustain some structural damage to the plates that will lead to early failure eventually, so it's something to be avoided.

A normal auto battery is designed to run between 50% and 100% charge for maximum life. It will self discharge at about 2-5% per month (assuming the electrical system doesn't add additional load due to snoozing electronics common in modern cars) if left alone; a trickle charger is intended to compensate for this low loss rate and charges at a similarly low rate. Starting the car will also cost about 2-5% each cranking cycle. It probably takes 10-15 hours on a charger (or alternator) to bring a battery up to 100% from low charge (depending on the capacity of the battery and age), so the typical charging system works to recharge at about 6-10% of the battery capacity per hour.

So, if you start with a fully charged battery and drive it once a week or more, then 15-30 minutes of driving makes up for the discharge due to starting the car and the self-discharge is negligible. But if you drive it once a month for 30 minutes, or start and restart it often with a few miles per start, then you would be on the deficit side as far as charging is concerned and not be fully recharging it and eventually end up at 0 charge. An old battery probably loses more and takes longer to charge too.

As far as battery discharge at low idle, once you start the car, the car should be running mostly from the alternator and only be draining the battery if you have an unusually high load (fan, headlights, stereo, etc) and low RPM (so if you're worried, start turning unnecessary things off). Otherwise, a good drive (such as down to Monterey) should fully charge a good battery and you shouldn't have any problems.