I suspect your charger isn't up to the job, mine wasn't either which was why I ran the battery with the charger connected, only trouble with that is over a couple of days the battery goes flat cos the charger cant keep up, hence my move to a psu.
If you want a really fancy PSU conversion then there's a guide here
http://www.wikihow.com/Convert-a-Com...b-Power-Supply
I just cut all the yellow wires and joined together (+) and all the blacks (-) in a terminal block, the 250w psu is rated at 16amps continuous over 12v and never even got warm plus it has built in overload and short protection so gives a bit more piece of mind when leaving unattended.
Oh your going to enjoy cleaning the electrodes
and if that saw blade is stainless make sure its all ventilated and wear gloves with the electrolyte as the chromium released from the stainless is apparently quite nasty.