Sorry for the following long post, but ask a complicated question & get complicated answers…

A properly used stiffening cap is to your electrical system, what your shock absorbers are to your suspension. You could drive your car without shock absorbers but the constant pounding will ruin structural components & transfer the shock to the rest of the vehicle, causing your pc to shut down among other things. The stiffening cap will actually prolong the life of your alternator in the same way, by "absorbing" the big instantaneous demands for high current & smoothing them out to a certain point. Just because your caddy has shocks, doesn't mean you can go Baja it off road, obviously a stiffening cap isn't going to cure all & if the overall average draws of the system & the rest of the vehicle is higher than the output of the alternator the cap will not solve your problem. you can't expect a stiffing cap to supplement a true 1000+ watt system, & even a bunch of batteries will only prolong the inevitable of draining your reserves, to run a system that has big power demands you must increase the output of the alternator to meet these demands.

The best solution is a combination of an aux battery close to the amps & a stiffening cap. A configuration like this will allow you to draw up to & even over your alternators output for short periods of time without a problem....


I can't tell you how many bigger systems have been installed, only to need a new alternator within a month or so. This is actually common, especially if your working with a car that has had it's alternator in service for 5 years or more. The main goal here is to absorb the dips & spikes, the headlights dimming are only a symptom of the real problem.

An amplifier instantaneously pulling up to 150 amps or much more in some cases, from your battery for a peak is almost as severe as intermittently shorting the terminals. This will not only overload the alternator, but can also screw with ecm's, bcm's, air suspension and/or suspension controls, not to mention a whole host of other electrical systems in a vehicle, Including your car pc, which doesn’t like an unstable environment, especially electrically.

most of these systems are already being taxed by the fact that they are used in a mobile unstable environment in the first place, & most have been designed to live under these conditions, but add this much more stress & problems can & do occur. This is the main reason that automotive computer systems use say a 5v reference for sensors & such, because they can regulate it & attempt to maintain this constant voltage much more reliably than if they tried to run these systems at full battery voltage, which can easily vary by over 2 volts up or down depending on loads & usage.


the cap can act as sort of a shock absorber, by providing the big instant hit of extra amperage at the right time, thereby taxing the electrical system that much less. Depending on how much is needed this may or may not make all the difference needed. an aux battery in the rear will kind of act as a spring, by being able to help deliver power under those same conditions, but for a longer period of time than a cap. The real difference is how "fast" the power demand is needed. Think of a cap as a sledge hammer, quick short bursts of power, but with a pause in between for recharging (backswing). Now think of the battery as a helper pushing. You will get the best results by having one guy pushing while the other swings away with the sledge hammer, all being perfectly timed by the physics of the demand at hand.

I have built pro systems that will run at say 1,200 true rms, & powered it more than adequate with a 4 gauge run from the front to the rear battery, which is close to the amps. From the rear battery you would give each amp the power it needs, with even a 0 gauge for the sub amp & cap bank, 0 gauge ground to frame. Now keep in mind that the 4 gauges only job is to charge the rear battery, which in turn really supplies the system. The 4 gauge will not be overloaded because on average it is only providing the 30-50 amps required to maintain battery voltage in the rear, & the majority of the quick instant heavy short loads are handled by the rear battery & caps, never actually overtaxing the front of the vehicle itself. This is verified by the fact that I can run this system with an 80 amp breaker inline front 4 gauge without ever blowing it. Actually the only way to blow this 80 amp breaker is if the front battery went dead & then I tried to crank off the rear battery, or boost the vehicle from the rear. This system had a peak draw of almost 200 amps & it never saw the front of the vehicle.

Anyone who tells you that a battery is better, or a cap is better, is not taking the whole picture into account. If I had to choose between one and the other in an install, I would pick the battery, but honestly they work best together. A batcap is kind of a melt between the two, but doesn't achieve the peak benefits of either; sometimes it can be a reasonable compromise when space is restricted...

I think some people here are missing the definition of deep cycle. Deep Cycling - The process of drawing a high percentage of a battery's capacity (deep discharging) and recharging it to full capacity. Any battery can be deep cycled but unless it is designed to it will not return to full capacity.

sdashiki....would you add a second battery to your car if it was stock? Obviously there is aftermarket electronics in the car to warrant a second battery. All to often people add another battery to the auto in hopes of fixing low voltage or lack of current in the system. That is the job of an alternator. Now when you add a second battery your alternator must keep the car running and both batteries charged even if there is an isolator. Let's say your alternator was running full capacity for 50 % of the time before installation of electronics and second battery. Now it must run full capacity 85 % or greater with the addition to the vehicle. yes the alternator might be able to handle but it will not last. It will generate alot more heat which will then cause it to fail prematurely. If you want the most performance and reliability out of your auto's electrical system then an upgraded alternator needs to be used...period.