Seems to be a theme around here, old cars with old batteries. But in this case Zippy was a little funky starting sometimes - it didn't really crank over, but it would still start. Since Mrs P drives it the most, I want to make sure she can get to and from places without drama. So it was time to check this whole thing out.
The Beetle's battery is 'famously' under the back seat. It's actually a great location, close to the starter and good for weight distribution. The only real downside is that the battery box is a frequent rust item and in extreme cases your battery can fall through.
When you start your car, a relay connects a very thick cable from the positive terminal on teh battery to the terminal on the starter. The cable needs to be thick because the starter draws a lot of electrical current. A poor connection there, or from the battery to ground (the chassis) can stop a car from starting.
Tools:
Wrench to remove battery terminals, I think mine were 12mm?
Steel wool / brass brush / etc to clean contacts as needed
Dielectric grease to protect the connectors after assembly
Vacuum to clean under the seat (rust, leaves, and other surprises)
Parts:
Group 42 Battery. (double check your year and model to be sure - Zippy is a 1974 Super Beetle Convertible) The Group number defines the physical size of the battery, along with terminal location and type. In our case it is very important not to get a battery that is too tall as it could short against the seat springs which are below the rear seat.
Step 1, remove the rear seat (just pull it up, forwards and out. There is nothing holding it in.
The negative terminal has the wide braid, the positive terminal has insulated wires. This is pretty normal for almost any car. The negative terminal gets bolted to the frame or the engine usually. There is no chance of it short circuiting. There is lots of dirt and leaves and rust to clean up. Note the orientation of the old battery so you can install the new one the same way. Normally there would be some kind of hold down clamp to also remove but not on this car. You do not want the battery flying loose in an accident so normally they are bolted in pretty tightly. I'll find out what the Beetle's should have and update this.
Next, unhook the terminals and remove the battery.
For reference, the old battery has date code indicators but they were not used so there was nothing visible to me until I removed the battery completely. It should be easy to know how old your battery is.
Here is the new one, I asked the gent at the shop to mark it on top. They have stickers but I suspect most folks don't know to ask.
You can see it is a group 42 battery (MT-42) and the install date is 6/24.
The forward edge of the floor is pretty rusted out under the battery. This will need to be cut out and I'll weld in a new section.
Here you can see how dirty and rusty that ground connection it. We'll polish it up and protect it with dielectric grease so we have a great connection going forwards.
The old ground strap, pretty rusty. I used an electric drill with a brass brush to quickly clean it up.
Much better.
I used 0000 steel wool on the inside of the battery connectors to clean them up.
I used the drill and brass brush again to clean up where the ground connects to the chassis. This is probably the single most important connection in the whole car. Everything depends on it.
With the terminals and connections cleaned up I connected it all back up and then coated the outside with dielectric grease to protect it from water, dirt & corrosion.
Now zippy turns over and starts like a champ!
References:
Battery Group Number https://www.autobatteries.com/how-to-choose-your-battery/car-battery-group-size
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