Car Audio Power, Batteries and Wiring in Plain English
Every amplifier in your car is only as good as the electricity behind it: a steady supply lets bass play hard without strain, and the wiring decides whether the system is safe and reliable. Peter Steinbacher of Pssound, a UK high-end car audio installer, teaches that steady voltage matters more than extra amplifier power, and that most systems draw far less current than people fear. His routine: measure first, fix the supply only if it needs it, then fuse, ground and terminate everything properly.
The short version
Music is not a test tone, so a real system draws far less current than its amp ratings suggest, usually 20–80 A.
Check your voltage with a clamp meter before buying bigger amps or a bigger sub; Peter worries below 12.5 V.
Many sound-quality cars need no electrical upgrade; if voltage sags, go in order: a good front battery, a power run to the back, then a second battery near the amps.
Check a lithium battery's current cut-off, and charge it through a 30 A DC-DC charger, Peter's safest way.
Fuse the main cable within 40 cm of the battery, fuse again whenever the cable gets thinner, and upgrade the ground as much as the power cable.
Ferrules, solid grounds, XT60 plugs and keeping power away from signal cables help prevent faults and noise.
Good wiring takes days, and neat braiding is for competition marks, not for sound.
How much power a car audio system really draws
Amplifier ratings show the most an amp can deliver, not what music asks of it. Music rises and falls constantly, so readings from a clamp meter (it reads the current in a cable without cutting it) land well below the paper figures. Continuous signals such as test tones are the exception.
On paper, the VW Tiguan's roughly 1.5 kW RMS of amplifier power works out at 120–130 A. Peter expected no more than 60–70 A on real music, because every channel never plays flat out at once (watch).
A Porsche Taycan with a three-way front and two 15-inch infinite-baffle subs (mounted in a sealed wall, with the boot or outside air as their box) held 13.4 V, drawing 5–6 A at a comfortable long-drive volume and 10–12 A a step louder (watch).
Bass is what draws the current: the Audi RS6, playing music with crazy bass, drew 98 A at most. Infinite-baffle subs take very little power (see our subwoofer and infinite-baffle guide).
Measure your own system and watch the voltage. Below 12.5 V Peter would start to worry, and a big bass system under 12 V needs serious money spent on the supply (watch).
What the car can supply, and when to upgrade
Peter puts voltage first and power second: "If you want good bass in a car, sort out your voltage" before you decide you need a bigger sub (watch). For big setups he rates the supply above the choice of amplifier (see our amplifier guide).
A 120 A alternator does not give you 120 A to play with: the car's own aircon, lights and fans come first, so realistically 50–60 A is yours, which he says is enough for a sound-quality system even at full tilt (watch).
Many sound-quality cars need no upgrade at all: the VW Transporter T6 runs on its factory battery and alternator, and only SPL competition is different.
If voltage does drop, the order is a good front battery, a decent power run to the back, then a second battery close to the amps (the easiest option). Anything beyond that is a big investment (watch).
If you cannot fit another battery, a DC/DC power stabiliser (a box that holds the amps at a set voltage, such as 14 V) is worth it; in a BMW M5 build it regulates rather than adds capacity (watch). Capacitors are rarely needed with good batteries.
Electric cars are the easy case. The Taycan holds a solid 13.4 V, and playing its system for 8 hours cost only about 4% of range (watch).
Choosing a second battery: AGM or lithium
An AGM is a sealed lead-acid battery, the usual front-battery upgrade. Lithium holds its voltage better: a full AGM sits at only about 12.7 V and drops quickly, while a lithium floats around 13.2–13.3 V. A second battery near the amps is never a bad thing, Peter says, if sized sensibly.
Do not oversize it: the Ford Focus ST500's 100 Ah lithium was more than it needed, and Peter says even 50 Ah linked to the front battery would do (watch).
Check the battery's current cut-off, not just its amp-hours (Ah). The Mercedes E-Class's 100 Ah lithium allowed 115 A for 10 seconds; at 120 A its built-in protection shut the whole system down for about 20 seconds (watch). The RS6 got a 75 Ah lithium good to 280 A instead. Choose for the peaks.
Fit it rigidly: a battery boxed in behind a wooden wall cannot fall out but still moves in corners, which Peter calls a poor way to secure it (more in our fabrication and mounting guide).
Linking and charging a second battery
You can link the second battery to the front one directly, or isolate it so the car only sees a small, steady load.
Linking a lithium straight to an AGM works, despite the warnings: Peter's Honda Accord has run a 70 Ah AGM and a 60 Ah lithium linked with no relay for over six years (watch). Its smart charging (the computer deciding when the alternator charges) is less sensitive than in the newest cars.
The risk is a flat battery: drain the lithium, start the car, and the alternator can struggle to refill it, while a lithium takes in current eagerly. Makers advise about 50–70 A at most for charging.
Peter's safest answer is a current-limited DC-DC charger, a box that tops up the second battery at a capped rate. In the Skoda Superb and the ST500 it is a 30 A unit, less than switching on the car's own consumers, such as heated seats (watch).
The catch: it only works one way, so an external charger on the lithium side will not charge the front battery.
Without one, watch the voltage: if a linked pair falls below 12.5–12.6 V, start the car and charge until it is back near 13 V.
Cable size, fuses and grounding
The fuse protects the wire, not the amplifier: if a cable shorts, the fuse must blow before the cable overheats.
Size cable from a chart of maximum current per cross-section; that maximum is also the biggest fuse it can carry (50 mm² is about 0 gauge, 25 mm² about 4 gauge). A 250 A fuse on a cable rated for 60 A will probably not blow, and the wire will melt (watch).
Fuse every time the cable gets thinner, because a short in a thin branch would not trouble the big front fuse. Peter: "you have to use a fuse every single time you downsize the wiring" (watch).
Put the main fuse within 40 cm of the battery, as EMMA sound-quality competition rules require, so a short at the firewall or in a crash cannot melt cable beside cabin plastics (watch).
Size cable to the real draw: his usual ratings are 250 A on a 0-gauge battery run and up to 125 A on a 4-gauge amp feed. The Tiguan's owner wanted 0 gauge all the way and was told it was unnecessary.
Size the earth for everything it carries: the car's own electrics share it, so add the factory earth to your new power cable (in the Kia, 16 mm² plus 35 mm² became a 50 mm² earth) (watch). Use a solid, structural chassis point cleaned to bare metal, not a spot-welded panel.
Keep every fuse easy to reach and bolted down: a hanging holder vibrates loose and starts melting, and a fuse under an amp rack means lifting the whole rack.
Terminations, connectors and routing
Loose strands and weak connectors cause more trouble than most people expect.
Ferrule every power, speaker and remote cable end (a ferrule is a small metal sleeve that keeps the strands together). It costs next to nothing and makes the system more reliable; signal cables do not get one (watch).
Household clip connectors suit a house, where nothing moves, but not a car: solder or use inline crimps.
For anything you may need to unplug, his favourite is the XT60, a plug from radio-controlled cars (the bigger XT90 suits thicker cable), which he calls always safe to disconnect (watch).
Through the firewall, the factory grommet is often the only route, but Peter prefers a gland (a sealed cable entry) in a separate hole, or a run under the car, checking from the engine bay first to avoid drilling into wires or pipes.
While the carpet is out, run every cable you might need later, including a spare optical cable, and leave slack rather than cutting to length.
Never let a rack or panel rest on a cable, and put a connector inside a door's rubber boot so the door can come off without anyone cutting cable.
Keeping noise out and the wiring tidy
Peter's view: properly done wiring gives no noise problem, and most trouble in a botched build comes from neglected wiring.
Never run signal cables (the RCAs) parallel with power. Keep power on one side of the car and rack and signal on the other, and cross them where they must meet (watch).
Make the first test of any install a rev test: rev the engine and listen. Revs in the speakers (alternator whine) mean something is wrong, so check the earth points and how the head unit is powered; in a big system, feed it from the amps' distribution point (watch).
Badly terminated RCA plugs cause dropouts and interference, so check every one.
Fit a master switch so the system does not depend on the ignition. Wire boot LEDs into the factory boot light circuit so they switch off when the boot shuts and draw no power from the system.
Spend on good connectors, cable and soldering, not magic: one car had power cable purifiers (plastic boxes tied to the cable) and pricey RCAs and still sounded bad.
Braiding is for competition marks, not for sound; a daily car needs a battery fuse, fuses to each amp, ferrules, heat shrink and labels. Wiring takes far longer than people expect: his S-Class took three days for two people.
Common mistakes to avoid
Sizing your electrics from amp ratings, or buying a bigger amp or sub, before measuring real current and voltage.
Putting a big fuse on thin cable, or relying on one fuse at the battery.
Fusing below what an amp needs: a 30 A distribution fuse on a midbass amp with a 60 A fuse built in blew during tuning.
Choosing a lithium battery by amp-hours alone, ignoring its current cut-off.
Earthing to a thin spot-welded panel, or using an earth smaller than the power feed.
Leaving a fuse holder hanging loose, or fuses buried under the amp rack.
Running power and signal cables side by side, or buying cable purifiers instead of good connectors.
Watch Peter explain it
This is an independent, plain-English summary of Peter Steinbacher's public YouTube videos, written by VA3 Car Studio. It is not affiliated with or endorsed by Pssound. The links jump to the moment in each video where he makes the point.
Part of our series: Car audio lessons from Pssound, start here
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