So many battery chargers are capable of some form of battery testing or estimating a batteries charge. But many are misleading as well.
A bad battery can have a good surface Voltage but not enough output.
With any electrical system problem, you start by verifying the battery is good. A poor mans check it to put a Voltmeter on the battery terminals or the under hood jumper terminals and measure the battery Voltage at rest, then turn the headlights on for 2 minutes and see how low the Voltage drops.
If you do not have a Voltmeter you can use the Hidden OBC Menu and display the Voltage directly on the dashboard.
BMW X5 - Access the Hidden Onboard Computer (OBC) Functions.
Also what happens if you attempt to jump start the vehicle?
I also keep something like this in my car as well -
http://www.amazon.com/CP-02B-8000mAh...ni+jumper+pack