In my case, I'm getting to the upper end of what the factory pump can supply, I'm pushing the ignition system much harder than ever intended. I could compromise and run a smaller plug gap due to higher boost but that compromises other engine tuning characteristics that I'm not will to sacrifice so I could invest a lot of coin into another ignition system, I could spend a lot of coin on a bigger fuel pump or as I have done, I spent about NZ$4 on this little mod and can get just a little more from what I already have which gives me a safety margin.
Your major concern seems to be with cooking batteries, I don't think this will be a major issue with a small bump in system voltage but I guess only time will tell.
@immortality thanks I got it - in your case you have reached the limitations of the system and need a safety margin. Fair cop - easy and cheap mod for you needs. I am not overly concerned with cooking batteries - it is something you have to be aware of. If you bump the system up to 15+V you should be thinking about the benefit. If you are under 15 i'm sure the battery will survive.
There's no shortage of amps. What I'm losing is voltage. I'm losing tension because I'm adding more current (there's the laws). Now add a bunch more systems and I'll eventually drop to an unhealthy level to keep my battery charged. I only need a couple amps but what I really need is voltage.
@Pollushon I get where you are coming from. I have not said there isn't enough power - amps or volts to go around - although I did use an example to try and illustrate a point about what would happen if you exceeded the capacity of an alternator. I am also not saying the mod doesn't work.
As for overcharging a car specific SLA that's ridiculous. I don't think you understand the type of battery it is. The higher end of the power spectrum will prolong its life. If you've ever used a battery recovery charger after calcification has corrupted it you'd understand what I'm talking about
I assume you are referring to reversing sulphation by providing a prolonged charge aI 15-16V. This is to reverse the effects of a battery that has been undercharged by a poor charging system or numerous short runs without fully charing the battery.. If the vehicle is being run for more than half an hour the best charge method is to apply a constant voltage of 2.40–2.45/cell (14.4 -14.7V). If you are keen and then want to put it on trickle charge overnight to prolong battery life it should then float at 2.25–2.30V/cell (13.3-13.8V). If your system is operating within 14.4 -14,8V, and there is no other specific reason you need a boost, there is no need for any electrickery.
I did provide an example of how adding tjhis mod to a system that is healthy could have detrimental effect on the battery. On short runs you are right 15v may be beneficia; however, if you do prolonged runs during daylight hours you can provide too much. I simply showed how adding a diode to a healthy system could exceed this limit. I am not focussed on it - just trying to show real world examples of how it could go wrong
I have tried to steer away from terms like ergs, and sag etc by focussing on the electrical principles. It appears that tying to use well defined terms in context has confused some.
So
The question I asked was simple - why would you do it. After all of this discussion I only have a few valid answers.
1. Your charging system is not great be this due to age or failing components. The mod will prolong the life a little longer but eventually you will need to fix the underlying problem, that could be realated to an earth side voltage drop, a poor regulator, failed/failed windings etc.
2. You are at the high end of the performance scale (be it spped or loudness haha) and the voltage drop due to load affects performace - eg pumps, ignition systems ect. This will only be an issue for a select few.
3. Dual battery system to overcome the VD caused by the isolation diode.
On the down side - if you already have a healthy system this mod may be detrimental to the overall health of the battery.through overcharging.
My conclusion is that this mod may be worthwhile for some but unless you are pushing the system to its limits it is not something required by the majority. If your system is in good shape it may even be detrimental. I will leave it to you to make up your own mind.