battery drain on 1998 Forester

[Les]

Appears have slow drain of battery on1998 Forester. New battery installed 12/2015, and also new alternator. Car sat then until 6/2016. Has been recharged twice since then, fully, on slow charge/48 hours. Connecting ground cable show moderate spart initially, and on subsequent contact to post shows weaker spark. All switches, doors, etc are in no demand position. What next? 

[Rooster2]

Since car sat without starting for 6 months, I am not surprised that the battery went dead. Even though not running during that time, there is always a small amount of continuous battery drain through the car electronic systems. It would have been better to have run the car a few times during that 6 month period, just to keep the battery charged, and oil circulating through the motor.

 

If the battery went dead, and was exposed to freezing temperature, it is possible that the battery has gone bad. Frozen dead batteries don't recharge very well. Suggest you find the battery receipt, jump start the engine, and return to where you bought the battery. Someone at the store will be able to test the battery, and tell you if the battery is good or not. If it has gone bad, you will have your receipt, and should be able to get a new battery for free, or at low cost.

 

Under the circumstances, don't think any system on your car is a source of a battery drain.

 

In the future, if car is left for 6 months without starting, it is better to disconnect the battery cable to prevent discharging.

[1 Lucky Texan]

you can measure 'dark current' and pull fuses until you find the high-demand circuit.

 

even a new battery will degrade quickly if it has ever been completely discharged - and every time it has gone flat, more damage is done.

 

best to use a battery 'tender' (trickle charger) or remove a battery if it sits unused.

[Fairtax4me]

You will almost always get some spark when reconnecting battery cables on a modern vehicle. There are multiple control modules that will turn on immediately when the battery is connected.

The AIrbag control module has several large capacitors that require a fair amount of current to charge and that current flow will create arcing when the battery is connected.

 

It's not good for a battery to sit for long periods. The control modules in the car do create a small draw that is considered normal, but it will drain a brand new battery in about 3 months. Once a lead acid battery goes dead there is irreversible damage done to the battery. The extent depends on how long it stays dead. With frequent use you may still get a couple years of out of it, but it will not provide proper cranking amperage, and may not be able to provide enough amperage to start in cold weather. It will also discharge much more quickly between uses, even if it is totally disconnected from the car.