2004 ML wont start
 

My car wouldnt start yesterday .
AAA jump started car ,drove home, put charger on overnight.
Battery is charged 12.5V
when I turn keyto first stop all dash lights come on. (light check)
when I turn key to start , I here a relay trip and all lights go out (dead)
Rechecked battery and charge is good . Do I need to reset something.
Help!!! car just went out of warranty

Voltage means nothing if you don't have the AMPS to back it up!

Take your battery down to your local auto parts store and have them test it.

As Johnhef mentioned get the battery tested first. I've seen units with a defective cell that appears to take a charge but then that cell drops to zero volts under a load. You'll also see the voltage slowly dropping after removing the charger.

If the battery checks out fine then the most likely cause is corrosion in a wiring connection. Remove the cables (especially where the ground is connected), clean everything with a wire brush, and use sealant spray or electrical grease when reattaching.

If it is a bad battery and the store does not have an appropriate replacement you should note that MB roadside assitance will deliver and install a new battery for about a $60 premium over the battery cost in most places.

First of all, a fully charged battery will give you about 14.5 Volts with no load. I agree with the others, it sounds like your battery is not good. To me it seems that it won't hold a charge.

If it is the original battery it may be at the end of its life. I'd also check the connections on the battery terminals.

A good battery does not put out 14.5 volts. The alternator will charge at 14.5 volts, but the battery should be around 12.5 volts.

I would check your battery cables for good connections. Sounds like when you put a load on it, you loose the connection. Remove, clean, and reinstall your battery cables at the battery. If that fails to work, follow the cables to their first connection point and verify those are clean and tight.

You should also charge the battery, then load test the battery. This will tell you if the battery is good.