What would be the cause for battery discharge?

Called 'Paracitic drain'. Caused by something consuming power when it shouldn't. Take it to a good auto-electrician.

https://www.google.com/search?q=Saturn+drains+battery+overnight

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Cold temperature is discharging power from battery. There must be a temp differential between shop and outside. Regardless to where the battery is it should not discharge power that quickly you may need a new battery

Robert

After checking that there is nothing left on which could do this (you would notice) the likely causes are

- battery self discharging due to end-of-life
- fault in the alternator unit permitting discharge to earth

An auto electrician can see which very quickly

What I see here is " battery discharges if I leave it off overnight'
I assume you mean - not connected to the car and if so, you got a bad battery.
Fix it!

First step have the battery tested, a bad cell can cause a internal drain and kill the battery, if the batt is ok then check for interior lights like visors that stay on or interior light that come on by themselves at night due to defective door switches.

If you mean the heated seat then disconnect the battery ,leave overnight with the battery cables joined together as this will discharge the airbag module then remove the seat and strip the cover off of it

The battery will not discharge unless there is a drain. When the car is shut down disconnect the negative battery terminal. Put a DC ammeter between (in series) the battery negative terminal and the disconnected cable. The drain due to electric clock and immobiliser circuit will be in the order of 30mA (0.03 Amps). Remove each fuse in turn and note any drops in the current drawn. At some point you will encounter a fuse which when removed drops the current drain, it is this particular circuit that is primarily the cause of the battery discharging and it will need closer inspection to detect the fault within it. If you can leave this fuse out to prevent battery discharge.

If you can hear a click (quite loud) from the engine compartment, but the starter won't crank, this also could be caused by discharged battery. Battery problems - Discharged or dead battery is one of the possible reasons for a car not to start. Very common is the situation when we forget to turn the lights off overnight (the dome light, for example), which causes the battery to drain. In this case when attempting to start a car, all you will probably hear will be a clicking noise - there won't be enough power to turn the starter. Here is the simple way to check if the battery is discharged: Turn the ignition on. With the engine off, turn the windshield wipers on. If they move way too slow, much slower than usual, the battery is probably discharged. Also look at the dashboard lights - if they appear very dim, the battery is probably discharged.
If the battery is relatively new, it can be recharged. All you need to do is to boost your car and let the engine run for a while to charge the battery.

However if your battery is more than three-four years old, you will probably need to buy a new one. Sometimes, an old battery may even die with no apparent reason, even if the day before it was OK.

If the battery is OK, the starter solenoid, starter cables or the starter motor itself could be a problem.

Check it and tell us news.

Please check the cutout. Sometimes it does not disengage and thus keeps discharging the battery even after the vehicle has been switched off.

Try to locate the cause of the discharge current as below:-

While vehicle electrical system shutdown as for overnight storage, connect an ammeter (with suitable current capacity and sensitivity) across the main ground connection between the battery -ve terminal and vehicle chassis/frame - (-ve of the ammeter to -ve battery terminal post, +ve to vehicle frame),
Carefully disconnect the main battery ground cable from the chassis,
The ammeter will now measure the battery discharge current - a discharge current in the order of 0.5 amp or more is of concern.
If all is well, the current draw should not exceed 50- 100 mA.
Note- Do not switch on any load while ammeter is connected, as ammeter damage or overload will occur.
If an excessive discharge current is observed, remove all fuses etc to eliminate / locate cause.