2000 Saturn SC1 Battery won't hold a charge

What has ur keyless entry been doing?The best thing to do is test ur car for a parstic draw meaning a draw that happens when the car is turned off u can do it urself but u would have to buy the tools or have it done some where. Let me know what u find.

What model saturns is this a s model or ls model it will be helpfull to know so we can figure this out.

They have a tool that plugs into ur fuse holder with the fuse and tells u the draw of the circuit if u thought it was ur keyless entry or the body control module circuit which controls the keyless entry and it tells u the draw when the key is off. Or u could rig it up to hook to postive cable between the battery like it works with fuse to check overal draw of ur car.U can flip ur back seats down and see if ur trunk light is staying on also. That's about all tips to finding it I can tell u. Let me know what u find. If u don't find excessive draw then I would look at ur battery again even though they test good and are new I have seen them self discharge and not show up on a load test as bad.

The ECM is not plug and play it has to be programed u can't disable the alarm or keyless entry it's part of the body control module which u need that to start the car. How long does the car have to sit for the battery to goes dead?

Honestly I have never tried that or paid attenion if that happens and dont know if that is normal. But if u take the power away from a relay or ur bcm which has relays and switchs and they lose power and get power then yes it could happen when its getting power and everything is settling back to its normal state. There are so many things that could drain ur battery I had a car about the same yr as urs the tech tore the whole car apart couldnt find it. The car was passed on to me u know what I found draining the battery the master window switch in the center console who would have thought that.I unplugged the switch the draw went away.I honestly doubt ur ecm is drawing ur battery down I know its possible but thats a expensive gamble. Unless the guy that said it was bad will put it in writing thats it or he will pay for the computer. Its cheaper just to get a tool that will check for draws and start pulling fuses and unplugging things. They had that cool digtal read out one that plugs right into the mini fuse slot of ur fuse box and u could adapt it to fit the bigger fuses and to go on ur battery cable there like 25. Let me know what u find and what u want to do.