Plugged into the grid?

[ZugyNA]

I have an "AC Adapter" wallwart type transformer that was made to charge a 12V DC drill....that I've setup to try and charge the batt in my car.

I have a connecter from RS wired to the battery ...it hangs out of the grill down behind a driving light...so it might not get ice encrusted in winter.

Should just have to plug the transformer in and connect it for juice.

Works...but it seems to get a little warmer on the car battery than the drill.

INPUT: 96mA

OUTPUT: 400mA


Questions:

* what will it cost to run this over every 24 hrs...assuming an avg electric rate?

* what is the efficiency of this small transformer using grid power vs the car's alt?

* will it keep the battery charged?

* will it last...or will it overheat?

The battery probably needs replacing...does fine in summer...but if it sits in winter it will go flat.

I've heard that a failing battery can reduce mpg due to the alt constantly having to charge it.

True?