12V Guru – Poor Battery Connections

Question to 12V Guru: why are my batteries not performing?

We have just started travelling around WA after the various COVID lockdowns and have noticed that we were not getting the power out of our dual battery setup.  I checked the batteries and there was heaps of corrosion around the terminals.  Is this likely to be causing our issues and if so, can it be prevented?

Mark Able, Lower King, WA

12V Guru answers:

Hi Mark,

Glad that you have been safe over in WA and have been able to get your wheels rolling and get back out exploring. There are multiple reasons as to why your battery bank may not be performing to what you consider the optimal level. It is important to identify and address the cause as otherwise you are likely to experience a continued unnecessary decline in battery performance.


What you have observed as corrosion is an electrochemical reaction between the metal used for the terminals of the battery and the surrounding atmosphere.  As part of the internal chemical reaction to produce energy inside a lead acid battery, hydrogen escapes the battery case in microscopic particles from and this reacts with the terminal to create corrosion.  This corrosion can occur not just on the terminal but depending upon the quality of the connections in your cabling it may also occur on the exposed metal parts of the cable.  Your local environment may also impact the amount of corrosion – i.e. salt and moisture. The corrosion creates resistance and the flow of current affecting the ability of the battery to charge and discharge and therefore overall capacity which you can utilise.

What to do:

Safely remove the connections to the battery and undertake a simple cleaning process to remove the corrosion with a wire brush or sand paper. Apply a small amount of petrochemical to ensure a highly conductive connection to the terminals.  Suggest wearing a face mask to reduce nasty particles being breathed in during this procedure.

Loose battery connections

Loose battery connections are another possibility as to why it appears your batteries are not performing.  Loose connections can be a real problem as they are not always the root cause of the issue and the problem may be intermittent.  The main issue with loose connections is that it builds up resistance and current can not pass through the terminal connections sufficiently when charging or discharging. This resistance is expressed as heat and your secondary issue is then the potential for damage with overheated and melted wires.

What to do:

Suggestion here is to check the tightness of all connections and ensure that none have vibrated loose during a previous adventure.  This is probably a good time to check over all battery and terminal connections and ensure they are appropriately tightened.

Dual battery setup configuration

Another major cause of a system that appears to be failing, when the setup is a dual battery configuration, is that one of the batteries in the battery bank is starting to fail and potentially has a faulty cell. BMPRO’s recommendation is that when installing multiple batteries into a battery bank that they are all the same brand, capacity and age. 

We regularly see scenarios that RVers will have had their van for 2-4 years and then wish to increase their battery storage capacity and instead of purchasing two new batteries they just add one new battery to the older battery to increase the capacity.  The problem here is that the older battery will have a decreased internal flow of ions and therefore have a higher resistance. The higher resistance means that the battery current in or out will be low and reduce the overall functionality of the battery bank. 

What to do:

Perform a voltage test on the batteries fully charged individually (and rested for 30mins) or have an auto electrician perform a capacity check to identify if this is the source of your issues.

Mark, in summary – check your terminals and clean if required, check and tighten any loose connections and always build a battery bank with batteries of same, age, capacity and brand.

Safe travels

12V Guru

The article was written for Caravan World Magazine.

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