Have 04 Sprinter - batteries fully charged - lights and radio work but no cranking or start

All questions need 'year make model' please.

No, the alternator charges the battery when the engine is running, and it doesn't click.

Try this, put the headlights on and turn the key to start the car. Do the headlights go dim yellow like a glow worm? If it does, the issue is that the battery doesn't have enough amps to turn the engine and is just 'clicking' the starter motor...

Make sure you battery is fully charged before trying again. If it starts and drains again then you have an alternator that needs replaced. If it is fully charged and you still get nothing but a clicking then you need to replace the starter.

it seems like the battery is going. clean battery terminals, also the grounding to the body (engine block, transmission, etc.) all should be shiny cleaned. suggest you go to autozone (or other auto parts) for a free battery & alternator tests.

Try removing the battery cables and cleaning the post then making sure cables are tight

start with fully charging your battery.

Do you have any indication that the battery is not being charged properly, such as slow cranking speed when trying to start?
With the engine not running, the battery (fully charged) should show about 12.5 volts with a voltmeter. With the engine running at normal (not idle) speed, the voltage should be 13.5 - 14.5 volts depending on the state of charge of the battery. At idle, the voltage may drop below 13.5 volts depending on how many accessories you have turned on (headlights, a/c, blower motor, radio, etc). If the 12.8 - 12.9 volts you referenced is at idle with accessories on, but increases when you increase engine speed, you're probably OK.

Hello davidoz,

Your description sounds like a bad battery. Do you have a volt meter to watch the voltage as you turn the key to start? The voltage on a good battery( meaning fully charged) should stay about 11 volts while cranking, if it drops below that suspect a bad battery.

Another possibility is that the battery is good but the alternator is not charging.

Will it start with a jump? If is does check with a volt meter the out put of the alternator it should be 13.8 volts or slightly higher.

Regards,
netvan

Change the battery, your battery gone bad, and isn't fully recharging itself, and isn't havn't the min cranking amp require by your car to startup the engine, however there still enought charge in there only to power windows, radio etc. When starting a engine, you need at least a min cranking amp, and requires more when it's cold outside.

Make sure battery has a full charge and battery connections all good. Any fuses in the diagram, test for voltage, some are hot all the time, some go hot with the key on.
Use a digital multimeter across battery posts, everything off, the generic spec for a full charge is around 12.6 volts. Leave the leads hooked up to battery, have a helper turn key to crank, how far does it drop? In my opinion it shouldn't drop much under 10 volts, I wouldn't argue with 9.6 volts.

Start the car and when truck runs disconnect one of the Battery terminal, if engine quits You need an alternator