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Posted: Mon Oct 03, 2011 10:09am

Post Subject: Battery Management

Hi Folks, I recently had to change my 4 domestic batteries as their sides had bulged, I believe the term is blown, after an engineer advised me that they were in a dangerous condition and liable to explode. He was unable to explain why they were in this condition. It has been suggested that the cause is overcharging. The batteries and the boat are less than 2 years old. I'm running a Barrus Shire with two alternators; the starter battery is ok. In the last two summers we have completed around 1000 hours running time on the cut. When moored in the marina we are connected to the mains to trickle charge the batteries through a 3Kw inverter. Is it possible that overcharging caused them to blow via the alternator or inverter. Your thoughts would be welcome. Many thanks Ken


Posted: Mon Oct 03, 2011 12:42pm

Post Subject: Battery Management

My understanding of the cause of battery cases swelling is that the batteries have sulphated. When a lead acid battery is discharged lead oxide turns to lead sulphate and lead sulphate takes up more space than lead oxide. If the battery left in a partially discharged state for a period the lead sulphate becomes harder and harder until it is not possible to reconvert the lead sulphate to lead oxide without damaging the battery. I do not recognise the term "blown" and as long as the battery is kept topped up to the correct level an explosion is not very likely. If you only have an inverter it will not charge the batteries so the lack of charge is the likely cause. However if you have a combi-unit that is a charger and inverter in one case the charger function will be multi-stage which means that it is very unlikely to damage batteries. However such chargers can be set for different battery types and if yours is set for the wrong type of battery it could overcharge gel and certain AGM batteries. I would have expected overcharging would cause the plate material to fall into the sediment traps in the bottom of the case and eventually cause an internal short circuit leading to a faulty cell/battery. I would not expect this to cause the case to swell. Without far more information about the battery type and make, your electricity use and charging regime when out cruising I can not help more. My suspicion is that you may be over discharging the batteries and not fully charging them whilst out cruising. Tony Brooks

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