Take it easy, do your best to not allow wheels to break loose, don't push it going fast, test for traction often by stabbing the brakes or nailing the gas momentarily. The moment they do lose traction however, you lose steering (love FWD don't you?), so your vehicle direction now goes the way of momentum (not what RWD does). If you feel them break, just back off, and apply gas again, similar to what the ABS does only do it on the gas.
The only problem with putting weight in the back on a FWD is it takes weight off the front end and you lose front traction, which is the only strong point a FWD has. For me? RWD with a posi is the only way to go, and you can go about anywhere in any traction condition. As you accelerate with FWD the weight bias shifts from front to rear, unloading the front tires, losing traction. So adding weight to the back adds to this. The battery isn't too terribly heavy, but very heavy for its size. And the biggie is how far from center of gravity it is. It acts as a lever, making it more effective the farther away it is. It hurts dry handling on FWD, but helps snow/wet traction.
Best? Add sand bags to the front end, but you sure look silly... On FWD I get the largest battery I can. On RWD I relocate the battery to the truck. You can't imagine the traction improvement dry/wet with the battery in the trunk on a RWD car. Even w/o posi it is great. The MB S430/S500 (2000-up) and RR and Bentely's have them in the back factory, balances out the car a lot.
Honestly, having a set of the new modern snow tires such as the reasonable priced Winterfires (tirerack.com has them for $57ish each) is by far the best investment if you live in a snow climate like I do (Wisconsin). And I drive 50 miles each way to work and back, often on back farm roads.
Tirerack also has them mounted on steel rims so you don't have to mess with your existing tires/rims.
Oh, on carpet strips? Make sure they are long enough to connect the front and back wheels, if not, they just spin out from under the tires, as the stuff under them is often slick and as soon as you hit the gas, away the carpet goes! It will shoot it for 10-20 feet away from you. So you need a long strip to make it work. Been there, done that....