Battery Beware!

Corrosion Problems

Continual problems with battery terminal clamp corrosion on my Chummy has prompted me to share some issues with you about construction, safety and prevention.

The reason for corrosion is due to the battery acid attacking the brass of the battery clamps.  This can be due to one or more of three causes.  First, poor construction of the battery where the seal around the posts is inadequate allowing acid to creep up to the clamp. Second, where sideways stress on the battery post has been caused by vibration or movement, and finally, acid vapour from overcharging. 

Looking at the issue of stress on the positive and negative posts, if your battery is not firmly clamped or wedged in its box then it can move about only to be restrained by the battery leads connected to it.  If these leads are the old original heavy duty copper cable, then they will provide considerable opposition to any movement and the strain will be taken on the battery posts which will ultimately destroy the seal and corrosion will set in.  If you are doing a rebuild or upgrade, it is a good idea to replace your old cables with double insulated welding cable which is flexible and can accommodate movement. It is important that every connexion on a main battery circuit is soldered because clamped or crimped terminals are a definite source of trouble! 

Overcharging from our Sevens is a common cause of problems, as most of us on winter charge put in at least eight amps continuously regardless of battery voltage, so the excess amps are dissipated in gassing which causes acid vapour to emerge through the vents over the top of the battery.  Modern cars normally don’t get the problem because their charge is regulated by battery voltage and for the most part use “sealed” or better described as “valve regulated” batteries.

Safety Issues

Looking at battery construction there are some safety issues. Most of us with 6V systems use a single 421 MGB battery, two of which are used in series to supply the 12V for an MGB.  My current battery (with all the problems!) is a Lincoln with exposed connecting bars between each of the three cells – very original looking and widely advertised, but also can be a severe fire risk!  With all the tools and spares we carry it is so easy to short out one or more cells when they are connected by bare lead straps on top of the battery, in fact you can even do it with battery charger terminals!  To minimise this risk I have made up rubber covers for all the connecting bars but I think in hindsight it is best not to use this type of battery in the first place unless you are a real originality purist.

It is important not to use a modern “sealed” battery on an unregulated charge output from an Austin 7 due to the amount of gas produced by overcharging.

Corrosion -  Removal and Prevention

Before you tackle corrosion make sure you are using eye protection and protective clothing including rubber gloves. Make sure the battery area is well ventilated and each filler plug has been unscrewed (but not removed) to release any hydrogen gas. You can carefully remove as much corrosion as possible with a short blunt screwdriver and then use a light industrial vacuum cleaner to remove the debris (typically a “Henry” but not the household Dyson!).  Next carefully undo each terminal clamp and take each terminal off its post.  Carefully cover the top of the battery and the surrounding area and place something under the terminal to catch debris and liquid while you are cleaning.

The remainder of the corrosion can be removed with a small wire brush. Next a strong solution of bicarbonate of soda can be used to neutralise the areas of corrosion on the clamps.  It is important to carefully wipe away any traces of bicarb solution as it can also cause corrosion.  Ensure the corrosion has not weakened the post terminal clamps or their clamp bolts.  Replace any components as necessary and don’t forget to solder any new terminals  even if they have cable clamp screws!  Next, its time to get bright shiny metal showing on each battery post and on the inside contact area of each terminal clamp.  This can be achieved with emery cloth and a small wire brush or you can get a combination battery cleaning brush, one part of which is a male conical wire brush for the clamp and the other is a female conical brush for the battery post. 

Having got everything nice and clean you can spread a layer of Vaseline around the base of each post and over the bottom of each clamp but keeping it away from the metal to metal contact areas.  Once the clamps have been replaced and tightened, the job can be finished by a further liberal coat of Vaseline over the exposed areas on each clamp, the idea being to totally cover all surfaces so as not to allow any exposure to acid vapour. You can also help the situation if you have summer and winter charge positions on your ignition switch by using it to reduce the charge at any time when you are satisfied your battery is charged up ( but don’t forget to change back to full charge for night driving!)

If all else fails then perhaps it is time to consider an upgrade to a 12V system using an electronic voltage regulated circuit and a modern 12V sealed for life battery! 

Safety Warning

 This article is not intended to be a definitive instruction and has been written solely for interest purposes.  Acid is corrosive, hydrogen gas from overcharging is explosive and the soldering of battery circuit clamps and lugs may require the use of a blowlamp and should only be undertaken if you are experienced in soldering and able to perform the task away from the vehicle.  Any activity arising from this article is at your own risk. Phil Whitter DA7C