For some reason my battery goes flat after 3-4 days if i dont drive it.
Checked all lights and such, so not sure whats going on.

This all started when i had an aftermarket immobiliser/alarm fitted (dynamco brand).

Do you reckon it was fitted incorrectly? and just drains power out somehow, more than normal?

Have battery checked as it may well be on its way out, go back to alarm fitter to see if there is an issue.

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Race Torque Dyno 399 NM, 248Kw @ 20PSI

Straight roads are for fast cars, twisty roads are for fast drivers. I have or am neither.

http://tttmsp.smugmug.com/

My last battery was still in warrantee, so they gave me a replacement and this new one is doing the same thing, so it sorta rules out the battery itself.

I took the car back to the fitter which was Hobart Car Audio but they said it was fitted correctly and didnt want to relook at it without charging me.

Doesn't rule out the battery at all, they can fail at any time...
Need to carry out a current draw test and see if there is any draw on the vehicle

maybe you have a faulty Alternator

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race tape y pipe running .05 bar till spares turn up.

Don't think that would cause the battery to flatten in a few days if the car is stationary/unused. But if driven and the battery goes flat, it would point to this.

Best to go to your local auto sparkie.

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Race Torque Dyno 399 NM, 248Kw @ 20PSI

Straight roads are for fast cars, twisty roads are for fast drivers. I have or am neither.

http://tttmsp.smugmug.com/

Do a resistance check between your positive terminal and the chasis with the car switched off. Sounds like you may have a partial earth.
Set your multimeter to the "Ohm" setting. Hold one terminal on positive and the other on a nice clean bare section of metal (Engine block would be good)
Reading should be over 100M ohm. If its significantly less than this you have a partial earth and the battery is slowly discharging to earth through the chassis. Also check all your headlights, tail lights and indicators, if they are flooded or have water in them that can also cause earths.

It may also be the battery. If its quite old you may need to get a specific gravity check. The electrolite might be shite.... Normally when lead acid batteries get old you have to do whats called a 'gassing charge' on them which involves overcharging the battery. Its easier just to get a new battery.

If the new battery goes flat in the same manner, its defiantly the problem that i stated earlier.

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STi Ver 6 | 2.1L Stroker | 418whp | 11.5 @ 199kph |

Not fast enough dammit!

Car starts and charges fine if its driven day to day, but as i have a work vehicle it only gets driven once/twice a week.

Gonna have to bite the bullet and pay some $$$ to get it sorted i reckon

Do a resistance check first mate. If its less than 100 Mohm, check your stereo...Most aftermarket stereo setups tend to have power fed to the stereo via a direct feed from the battery and bypasses the accessories relay which causes the discharge. Any sections of wire that are spliced together, make sure they are heat shrinked or appropriately isolated with electrical tape.
I promise you 80% of the time this tends to be the issue.

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STi Ver 6 | 2.1L Stroker | 418whp | 11.5 @ 199kph |

Not fast enough dammit!

Im pretty sure part of the stereo setup is direct connected to the main battery that goes flat. It connects from there to the RedArc, then to the boot battery.

I'll check out the Ohms tomorrow, see what i get