My positive terminal on my battery keeps corroding. I have tried switching batteries to see if it is the battery, but it has proved itself to be the terminal. I have a 94 Audi sedan, the battery is in the back seat (and why do they do that?) so the cords are quite tight and not long enough to attach a new terminal onto it. Should I extend the wires somehow? Is there something I can put on the terminal itself to prevent the corrosion? And if so, do I have to continually keep adding this? The corrosion builds up within 1 week.
Go to your local parts store, and purchase an aerosol can of battery terminal protector.
Clean the battery terminals one more time, and reconnect them. Now spray the terminals with the protector.
Tester
Have the alternator charging voltage checked. Auto parts stores are glad to do this check, in the car, free. A voltage too high will cause battery acid to vent and corrode the post/terminal. An over-charging alternator will shorten battery life.
Clean the battery terminals and the cable ends. After cleaning, tighten the terminals as necessary. Then smear the battery terminals with Vasoline.
The cable can be extended but IMHO it should be extended by soldering and not by the use of butt connectors and cable lugs.
I also agree with having the charging voltage checked and spraying the terminals with protector.
The trick in the old days was to lay a penny by the terminal and sprinkle baking soda over the top of the battery, but haven’t seen that one in years.
I agree with the others, but let me try and offer an answer to your question as to why it is under the back seat. An engine compartment is a rather harsh place. Lots of vibrations, heat cold chemicals. Not a good place for a battery. Under the back seat may get cold but it gets less vibration heat and fumes.
Get those contacts really clean, coat them with some sort of protectant and check the charging voltage. It would also be a good time to check the electrolyte level. (Yea, checking the electrolyte is one negative about having it under the seat as is the longer cables. )
I still use this little trick for cleaning battery cable ends. In a plastic cup, like an empty yogurt cup, I put about a tablespoon of baking soda and add water to close to the top of the container. Stir it up a little bit. Now stick the cable ends, one at a time, into this mixture. The mixture will get cruddy, even a brownish color. Empty the container into a glass or plastic bottle or jar for later disposal. Mix up another batch of H2O/baking soda. Dip that same cable end again until all bubbling stops. That cable end (the clamp) is now clean. Rinse with clean water. Now do the other cable end. Same procedure. Clean the battery posts with a wire battery post cleaning brush. Some come with a metallic case others with a plastic case. Carefully brush off the corrosion from the top of the battery using a 1" or 1-1/2" “el-cheapo” paint brush into a small dustpan or other open container. A small cardboard box or the cut-out bottom of a plastic milk jug? Coat both the insides and outer parts of both cable clamps with petroleum jelly (Vaseline or equiv.). Place the clamps onto the appropriate battery terminals. Do the positive one first, then the negative clamp onto the negative post. This works on side post terminals as well. Coat the bolts’ threads with petroleum jelly. Just a light coat will do. The petro jelly reduces/eliminates air getting to these parts and reduces/eliminates battery post and clamp corrosion. Whenever working on or around a battery, always wear plastic carbonate goggles or regular reading glasses. Don’t let that stuff splash around—battery acid (hydrochloric acid) burns BIG TIME. I also always use latex gloves. The jar that you placed the spent solution in should be glass or plastic with a plastic cap. Empty plastic peanut butter jars work really well. Empty plastic bottles work well, also, provided that you use a small plastic funnel to get the solution into a soda pop or water bottle. Dispose of properly. That’s why I recommend a plastic lid. That battery acid solution will eat through a metal cap. Don’t forget to look for corrosion on the starter connection. That would be the positive (red) cable from the battery, onto the starter solenoid. Should you find corrosion, disconnect the negative terminal from the battery, carefully remove the bolt attaching the pos. terminal to the solenoid, (either firewall mounted or on the starter), clean the corrosion off, petroleum jelly these connectors up, and re-attach to the solenoid.
you could have longer cable installed use side terminals and have side terminal battery installed if it can be done side cables does not need
clean as much. one wekk to short of time for this problem there must be another reason. have a plastic battery box put trunk and run cables
to battery you will need holes into trunk no problem we install battery in street rods in the rear. question since battery is rear does the battery have the poper amps because of the distance to the starter.
Clean and tighten the terminal(s). Then coat them with Vasoline, as others have suggested. Cheap, but effective.