Its a 1 farad cap, it has been out of use for like 3 yrs, but its probably like 10 yrs old itself.
I only had the charger on it for like 5 min, max . Is it possible it just needs to charge more? maybe ill try that and see, i have a trickle charger i can put on it for a few days....
Im only runnin 600wrms sub amp so i figured the cap might eliminate the bit of dimming im having( big 3 done) but im not interested in buying a cap so if this ones no good i wont bother

 

It's not a battery It'll charge in seconds as long as it's supplied enough power. I'd put decent size wire on each terminal and carefully touch to each terminal of a car battery . Please note that currant stored in both the car battery as well as a charged cap can hurt you, burn holes in metal if shorted out. Also to note wires used to charge cap can get very hot very quickly so wear gloves. I'd first attach wire from + terminal on cap to + terminal on battery then touch - wire to battery - (expect a spark there is a lot of power going through that wiring quickly, You'll be safe with dry leather work gloves on). Now without letting that ground wire touch anything else, tape it up will electrical tape than remove + wire from battery and tape it up. Now wait (say an hour), now take your volt meter set it for voltage DC in proper range and measure voltage from terminals on cap. If it's equal or greater then measured battery voltage (you should measure this first by the way) your cap is fine but please note your meter will gradually drain power from cap (this is normal ,remember it's not a battery it's suppose to do this that's why we use them). If the your measured voltage is much lower you should replace it. I'd be surprised if you find a bad cap though. Good Luck .Rob

 

Electrolytic caps that have been in storage for a long time will often need to be "formed" before they will effectively store a charge. A few months ago I saw a motor drive blow up when the power was turned on for this reason. Try the trickle charge and let us know how it holds after a few hours.