Won't start. 2 fully charged batteries tried. Cleaned battery connections. Just clicks when turning key to "Start". Car stopped while driving. Towed home.

With a voltage meter see how many volts are at the starter terminal. If not 12+ volts you have a bad connection. Check connection at the starter solenoid. Does it have 12+volts? Short the solenoid. Does it put voltage to the starter?

Make sure battery is fully charged. Check all battery cable connections. Make sure they are tight and free of corrosion.

check your battery connections then charge the battery over night then check the charging system

If you turn key to START position, what is the sound, is it;
1. no sound at all means maybe starter problem.
2. only heard Tik sound means starter problem (you can add relay but it will still happen in future)
3. crank sound but not start means battery weak.

You can also try to move gearshift to N instead of at P position before turn key to START. if it work mean your car safety switch at gearbox not know which gear you're on.

can you hear the starter click at all take a hammer and tap on the starter if that works then you know the starter is bad, if you are comfortable enough take out the battery and the starter and take them to your local autozone have them tested just because a battery is fully charged doesn't mean that it doesn't have a dead cell or 2. They can test the starter also

the clicking that you hear is coming from the starter relay. sounds like your ignition starter switch or ignition lock cylinder is bad.

First if the engine turns over but will not start then i woould check for spark at any of the sparkplugs and if you have spark then check your fuel pressure.If you don't have spark then you have an ignition problem.

sounds like your battery is just low,, it doesn't have the amps to actually turn the car over fully, you have 2 options, get the battery charged, or try to get someone to help you with a jump start,, either way , once you get it started, take the battery and have someone do a LOAD test on it,, to be sure all the cells are taking a full charge

the battery may be fully charged but that doesn't mean that it doesn't have a weak cell, next time you go to start the engine remove all of the battery filler caps (if it has any) & get someone to look into the holes to see if they can see if any of the cells are bubbling,if any are the battery is faulty & needs to be replaced......hope this helps......cheers.
PS. don't get your eyes to close when looking into the holes of the battery,it might be safer to use a mirror.