How can I avoid overcharging a battery?

Never leave your battery connected to a caravan charger for more than the time required except if using a C-Tek charger or similar. Although the caravan charger system is sufficient, the technical disadvantage is it never fully charges the battery to its full capacity. The charge voltage is cut off prematurely at 13.85 volts. Whichever type of battery you use, the in built charger will give a maximum charge to within 80% of the batteries original capacity. Over a period of time, this can cause sulphation of the plates in leisure batteries, due to under charging.

Over charging occurs when the battery remains on charge after it has reached full charge (14.40 volts). Overcharging causes excess heat that can cause the plates within the cells to buckle and shred their active material. The battery will also react to the overcharge by producing excess hydrogen and oxygen as the water within the electrolyte breaks down. The water that is lost due to overcharging can be replaced in a non-sealed battery. In a sealed battery, the water loss is permanent and will drastically shorten battery service life.

All batteries are manufactured to provide a certain number of deep discharge cycles. A cheap battery could give a cycling life of between 20 – 300 discharges if you’re lucky. A Gel battery will give between 400 – 500 cycles and an AGM battery 600 – 800 cycles. A battery with a 5 year plus guarantee will generally give 1000 plus cycles.

If the battery was left discharged for a week or so, it is likely that it has become sulphated. This means that a permanent change has taken place, which may render the battery totally useless. A sulphated battery is scrap and will not hold a charge. In any event, a battery will not last forever and its life will depend on how well it is maintained and how often used. Another type of leisure battery made by some manufacturers uses carbon fibre in its construction, which is claimed to inhibit sulphation and will therefore give an improved performance and enhance its active life.

Always re-charge a battery after use and if the caravan is to be stored for more than one month, ensure the battery is removed and stored in a fully charged condition in a cool, dry place. Check every two months and re-charge if necessary to ensure long and trouble free battery life. A battery left below 12.4 V will deteriorate quickly and will not be able to be recharged to its original capacity. If charging the battery when removed from the caravan, do not charge the battery on concrete, this could definitely affect battery charge acceptance (Heat sink effect). Ensure that the premises are well ventilated. Batteries expel hydrogen when charging, and this is explosive. No smoking is the rule.

Self Discharge – In time a battery will lose its charge, even with no equipment attached. Modern batteries lose 0.1 to 0.2% of their charge per day at room temperature, even when new – hence a newly purchased battery may not be fully charged. As batteries age or temperature increases, so does the self-discharge rate. During storage, most manufacturers recommend a freshening charge once every two months or so.