CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Electrical shortage

What causes negative battery terminal to get hot and drain battery when trying to start? Ive checked battery, alternator, starter, and cleaned posts.

How hot is hot? There’s a lot of current going through that connection, and it will heat up some if your connection to the battery isn’t perfect, or if the cable connection to the terminal isn’t perfect.

You may need to put a new battery terminal on the end of the cable if it’s getting excessively hot.

Ive checked battery, alternator, starter, and cleaned posts.

How did you do those checks?

Did you remove and clean bothends of each battery cable.

You mentioned the battery draining. Could you explain that at little more?

Excessive heat usually means a bad connection which could be caused by a defective lead or internal battery connection. If it is inside the battery that could be real bad as it may cause an explosion.

Expanding on what others have said: Hotness is likely from a high resistance (see below) in the circuit somewhere near the terminal. As mentioned, make sure the battery terminal and the connector ring on the cable are clean. Then make sure the connector ring’s connection to the cable is clean (I had one car fail to start when that connection corroded thru). Then look for corroding wires inside the cable (near the battery end, because you say the hot spot is there); maybe detect that by checking cable continuity while vigorously wiggling and flexing the cable. Then you have to consider a failure inside the battery.

“High” resistance could still be less than 1-ohm, which you cannot detect with a simple multimeter. Even, say, 20 amps going through 0.1 ohm would give only a two volt drop. The starter would probably still run, but you would be disipating 40 watts in the connection. Ouch – hot!