alandchris

I found the black and decker bm3b 'battery maintainer' at home depot for 19 bucks - the directions say, while the battery is still connected to the car - to hook the positive wire to the positive post of the battery and the negative wire to somewhere metal on the car. In other words - don't hook the negative wire of the charger to the neg post on the battery.

Anyone know why this is, and what problem could happen if the neg wire of the charge is connected to the negative post "while the battery is hooked up to the car" ?

jedblanks

That's typically a safeguard to keep from damaging the connected equipment if the battery shorts out. Good practice to do this when jumping a car too.

jedblanks

Btw, in a normal scenario there is no difference between the neg post and somewhere metal on the car, as the ground wire is "grounded" to the metal car.

realcanuk

I remember reading that this is to prevent a spark and possible explosion if the battery was gassing. When connecting the second (negative) cable you can get a spark and its just safer if its not too near the battery.

EDinPA

Charging batteries produce explosive hydrogen gas. Exploding a battery full of acid in your face is no fun.

ricknyc23

why not just use the cigarette lighter adaptor that came with the unit?