Amp vs Battery vs Voltage rating.

Heathen Recruit
Aug 18, 2020
I've just bought an amplifier which states how much power it makes at a given voltage (13.4v). As this amp will be run from my second battery (max ~12.5v?), I'll never see the full potential of the amp, unless I run it directly from the alternator, right? If I'm only able to power the amp from this second battery, is there formula to work out how much power I can extract at a certain voltage?

Also, the amp recommends 'at least 150Ah of battery power', and two 200 amp fuses.

My second battery is 50Ah. Even if I only run my amp to half of it's potential, am I going to wreck the battery? Am I even going to reach half of the amp's potential?

I'm not able to get a larger battery just yet, so alternatives are not an option at this stage. I have to work with what I have.


Oct 26, 2012
Scottsdale, Az
Yes. It is.

It is connected via a voltage sensitive relay.
A typical voltage sensitive relay "vs relay" allows for it to connect the secondary battery to the main / battery @ say voltages above 13v, then you should have everything coupled together when the vehicle is running and the alternator is doing its job.

When the vehicle is shut off the "vs relay" should allow your main battery to keep from being depleted from anything running after the "vs relay".

Kinda simple explanation but you should have the same voltage (minus any resistance losses) before and after the "vs relay" when the vehicle is running.

Since music is dynamic your amp (current) requirement will vary quickly.

What exact amplifier are you hooking up?
Last edited:

hispls Veteran
5,000+ posts
10+ year member
Sep 10, 2009
Central Maine
I'm not able to get a larger battery just yet
You may or may not get by with just one additional battery on a 3K amp, really depends on variables we cannot predict and your listening habits. Never seen that brand of amp and I have no idea what board they use, but safe to say if you keep your voltage above 12.0V anything that isn't flea market junk should not be failing and even a lot of flea market stuff should be able to survive dips lower than that. Normally car amps are designed to function from 11.8 to 15V or thereabouts leaving some wiggle room for expected variance in alternator output or health of electrical system. Most car audio equipment will have protect circuitry that will protect or power down the unit when voltage gets outside of safe range.

You absolutely will NOT be able to get max power out of any amp if you can't provide enough current going into it, but depending on what you're doing you may well never see full power out of it regardless of how much battery you have.

None of this probably helps, but in short. Give it a whirl, keep an eye on the voltage, and do try to beef up your electrical system as much as possible ASAP to ensure best performance and reliability out of everything involved.

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