C.Battery Side Terminal Connections

Some reports have been received that batteries are difficult to charge when out of the car. These reports also indicate that bolts are being screwed into the side terminals of the battery to provide a terminal for the battery charger clamps. Similar connections are used for load testing. Unless used in combinations with a nut as described in Item 2 below, bolts should not be used, since the mating threads inside the battery terminals provide a very small contact surface with high resistance to current flow.
The high resistance can prevent adequate charging current from reaching the battery, creating the appearance of the battery not accepting a charge, or at the least requiring longer charging time. It also explains why some batteries are called bad when they are load tested, but are obviously good batteries when checked with proper connections at the terminals.

While there are many methods and adapters available from various suppliers used to connect to battery side terminals for charging and testing, the important thing to remember is that contact must be made through the lead pads at the face of the terminal, rather than through the threads of a bolt. The following methods may be used:

Figure 2 - AC-Delco ST-1201Battery Charging/Test Connections - Preferred Method:

1. The preferred method is use of an adapter charging tool, AC-Delco P/N ST-1201 or equivalent (refer to Figure 2). The adapter should be snugged up against the lead pads of the battery with pliers to keep resistance between the adapter and battery terminals at a minimum.

Figure 3 -Battery Charging/Test Connections Using Bolt and Nut:

2. A secondary method, which should only be used when the adapter charging tool is not available, is by the use of 3/8" bolt with standard threads (16 UNC) and 3/8" nuts with standard threads. Use only zinc plated (silver colored) nuts. Yellow (dichromate) and black/blue (phosphated) nuts are generally nonconductive. Use the following procedure to install the bolts and nuts (refer to Figure 3):

a. Screw 3/8" nut onto 3/8" bolt (1-1/2" or longer).

b. Using fingers, screw one (1) bolt into each side terminal until it bottoms out, and then back off one (1) full turn. (Do not tighten with wrench as bolts can be driven through case.)

c. Holding bolt, screw the nut down on the bolt until the nut is against the battery terminal lead pad. Snug nut with wrench. (Do not overtighten as nut inside battery terminal could be pulled out.)

d. Attach the charger or tester leads to the 3/8" nuts and follow normal charging and testing procedures. Using this procedure, the main charging or load test current is carried through the lead pads of the battery terminals and not through the the nuts inside the terminals.