battery sign on dashboard turning on

Hi, I just plugged my radio, my 500Watts amplifier and my subwoofer in my chrysler 300 2005. After maybe 10 mins of driving, my battery sign on my dashboard turns on. It says on until I turn off the car and restart it. I tried turning my car car off as soon as the sign appear, and restarting it and the sign goes away. I've looked up in the manual and it says that it turns on when there is a problem with the recharge. Is it normal ? is it because my alternator doesn't understand why my battery drain faster than when I didn't have a amplifier ? help me please !

It's probably your alternator, not the battery... If your 500W (RMS) amp is at full output, you are adding about 50 Amps of load to the system. If the alternator can't supply the required total current, its voltage drops from a normal of say 13.4V - 14.4V down to the battery voltage (~12.8V or lower) and the battery helps supply the total Amperage (ie, battery discharge). It's probably the "undervoltage" detected by your car's monitoring system because on the OEM vehicle it would only be that low given a faulty charging system or battery. If you can find where the voltage is sensed, it might be possible to add an RC (resistor - capacitor) filter to ride thru the undervoltage periods. However because it's after 10 minutes, I suspect your battery is discharging significantly. The alarm may be triggering at 12.5V or 11.5V etc which normally signifies bad charging or a faulty battery.     Otherwise to prevent the alarm turning on you'll need a bigger alternator, however it's possible a BIG 3 (wiring) upgrade might help (and it will probably be needed anyhow with any alternator upgrade). However the main concern is whether your battery is not being recharged sufficiently. IE - tho you may be draining the battery during low RPM or peak loads, maybe it's recharged by the end of the drive. That's where dash voltmeters else temporary monitoring with a DMM is invaluable.

ok so if I get this right, the best thing to do would be to add an extra battery or get a better alternator ?

Adding an extra battery is useless, it's the alternator that needs to be upsized to handle your added load. PS - read up on the BIG 3. That's adding additional (else upsizing original) grounds from battery to chassis & engine etc. Plus upgrading your alternator output to battery to main fusebox etc connections. If your alternator is borderline, that might be enough to solve the problem (tho that is doubtful). However it is required for alternator etc upgrades, and it generally improves the electrical system anyhow.

Before you condemn the alternator, check a few things. If the problem only occurred right after the install, perhaps there is a fault in the install. Disconnect the added equipment from power. Drive the car and turn on as many accessories as possible (wipers, headlights, rear defogger, blower fan). Does the problem still occur. Use a digital volt meter connected to a good chassis ground and a power source to measure the battery voltage. With everything on, engine running, the voltage should be close to 12 volts at minimum. If you increase the RPM's the voltage should rise. Normally the voltage should be around 14 volts at idle with most accessories off. If everything checks out, examine how you wired the system. The amp should get it's power from the battery positive terminal. Fuse it within 18 inches of battery. The amp ground should be short as possible and to a clean section of the vehicle chassis or metal body. Don't use an existing bolt, install your own new one. Make sure all connections and battery terminals are clean and tight. It seems too coincidental the problem only occurred after the install.sparky

Ok, so I'll take a look to see if the voltage is around 12V+­. If it's not, it means I need to change the alternator and get a bigger one ? correct ?

No. But I suggest you inquire on Chrysler forums. You may need a software patch that was issued for some 2005 models. Get your battery tested. If it's bad, determine if it's the long wiring or alternator problem or other problem causing the issue.