I would like to know if I can mount my sound system in my car.

My current battery is 45AH, and the problem is that I can't go higher than a battery with 50AH, because there isn't space for it on the battery spot near engine.

My question, will I be able to use my sound system upgrading to a 50AH battery or it won't even be possible?

I am not planning to play music with the car turned-off by the way, so the car alternator will help right?

I don't know the capacity of my alternator, but the car is a Chevrolet Aveo Bi-Fuel 2011 (T250 Model).

My sound system specifications are the following:

Amplifier 1: Gravity PS1000 - RMS power: 2 x 125 Watt 4 ohm - Max. power: 2 x 500 Watt 4 ohm powering this Subwoofer: Climax Hazard 5000 - 500W RMS - 1000W Max Power

Amplifier 2 (next buy): L2.210 - Class A/B 2 Channel Amplifier 70W RMS x2 @4 ohm

Amplifier 3 (next buy): EV200.2 - Class A/B 200 W MAX Power, 38 W X 2 RMS @ 4 ohm

My calculation result in a total RMS of 466W (2x125 + 2x70 + 2x38)

And according to this rule Total RMS Wattage times 2 (Inverse of Amp Efficiency) divided by 13.8 Volts equals Current Draw in Amperes (explanation below) I will drain from my battery 68 A [ my calculation was ( (250+140+76) * 2 ) / 13,8 ]

So concluding my question, what will happen if I use a battery of 50AH in my car? supporting all this system draining 68 A?

Thank you so much for your help!

  • 2
    \$\begingroup\$ If you secure a secondary battery in spare tire well, from accidental spills or damage, this will provide the buffer capacitance needed with short cables used for starter motors to Amp. It may put excessive stress on your alternator belt so watch out and ensure 150lb tension or as rated for new belt is installed and beware of 3 phase diode faults with an ammeter and voltmeter installed. Fusing is essential to spare battery with an oversized alternator installed with adequate capacity. \$\endgroup\$ Dec 4, 2016 at 4:56
  • \$\begingroup\$ Hi @TonyStewart.EEsince'75 thanks for your comment, I was trying to not use a secondary battery. Can you just please tell me what will happen if I use this battery to power the sound system while driving the car? in the worst I can't just turn the volume to the highest right? thanks! \$\endgroup\$
    – TiagoM
    Dec 4, 2016 at 5:08
  • \$\begingroup\$ Do you know how to use AWG tables on cable length for 80A? Then monitor remote voltage and supply current if not. \$\endgroup\$ Dec 4, 2016 at 7:36
  • \$\begingroup\$ hawso, then get 1cm diameterLitz wire or bigger flat braid. from battery to AMP \$\endgroup\$ Dec 5, 2016 at 2:56

1 Answer 1


The peak current you can draw from a battery is not directly related to its capacity in Ah. For instance, your existing 45Ah battery starts your car, and the starter motor probably draws north of 200A for a few seconds. If it does that, it will clearly deliver 68A peak.

So the real question is, how long will the battery and the alternator power the amplifiers at your listening level?

There are too many unknowns to give a real answer.

If the question is, 'I have 50Ah, how long can I deliver 68A for?', then the answer is 50/68 = about 45 minutes. However, that wasn't the question. Amongst the confounding factors are:

Your amplifier will not draw 68A continuously. It may do that at the peak, but it will usually be much less.

Your alternator will deliver some current so the battery will last longer ... unless it's a cold night and you're using headlights and all the electric heaters you can.

You would not want to drain a 12v car battery fully. Going regularly below 50% capacity shortens its life, and if you flatten it with music, you won't be able to start your car in the morning.

You mention in a comment that maybe you just wouldn't turn the system up loud. However, unless your electrics are instrumented, you won't know how loud you can set it.

My recommendations are

a) Install the system.

b) Plan for the continuous load to be supplied by the alternator, so the battery evens out the supply between traffic stops and loud songs.

c) Install a large 'audio capacitor' at the amplifier terminals, which evens out the load on the battery between the individual peak cycles of the loudest notes. This reduces the reliance of the amplifiers on very short fat cables to the battery, and the battery impedance.

d) Instrument the electrics. Install a voltmeter on the battery, and/or a current meter in series with it.

The current will give you an indication of whether you are charging or not, and by how much, but it won't tell you the state of the battery.

The voltage should be around 14v when the battery is fully charged. If it goes below 11v, turn the system off, you've really over-done it. If it's in the 12-14v range, you are using both battery and alternator, and the battery is not fully charged. I wouldn't want to see less than 13v shown on a voltmeter, especially towards the end of my journey when I had to start in the morning.

  • \$\begingroup\$ Hey @Neil_UK thanks for your great answer! Can you answer me two other things? \$\endgroup\$
    – TiagoM
    Dec 5, 2016 at 1:07
  • \$\begingroup\$ Do you think does it worth upgrading my current 45AH battery to a 50AH battery? I can't go higher than that on my car, sadly :( and I though that maybe 5 Ah won't do any difference, what do u say? \$\endgroup\$
    – TiagoM
    Dec 5, 2016 at 1:08
  • \$\begingroup\$ The other question is, do you think I can measure myself my current battery by myself? I just need to buy a voltmeter is that right? Is it expensive? Like 50 dollars or more? Thanks! Because maybe my battery is really not that good, I should change it even for only 5AH upgrade... Thanks!! \$\endgroup\$
    – TiagoM
    Dec 5, 2016 at 1:10
  • 1
    \$\begingroup\$ Voltmeter, not expensive, I've bought a bunch of these bad boys ebay.co.uk/itm/…. Don't be put off by the low price, they work, and surprisingly well. \$\endgroup\$
    – Neil_UK
    Dec 5, 2016 at 7:36
  • 1
    \$\begingroup\$ Don't bother to change the battery for 5 lousy Ah. There's a technical term for the difference, which is sqrt(f'all). Do change the battery for a new one if it's showing signs of age, or losing its charge, or more than half a dozen years old. While changing, get the biggest that will fit. \$\endgroup\$
    – Neil_UK
    Dec 5, 2016 at 7:44

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