Maximise Caravan Battery Life in Storage
Question: I have just read that I shouldn’t leave my 2 x 120amp AGM batteries continually connected to a smart charger - in my case a CTEK 25amp - if I want maximum life out of the batteries. The article says the batteries need to be worked i.e. used and recharged or, when in storage, leave fully charged, turn the charger off then top up periodically or as necessary.
Answer (David Bayliss): Thanks for the follow-up question to a previous article. The advice to ‘exercise your battery’ is general advice due to the wide variety of chargers and combination setups that we see installed in RVs worldwide. After extended periods of charging batteries while in storage over winter or similar, people regularly return to their van and find that their battery is swollen. Many chargers promote themselves as smart chargers, however often the software used to monitor and control the charging algorithm does not consider temperature of battery, exact chemistry such as GEL, Wet, AGM etc and has limited protection mechanisms when there is a failure inside the battery. Charging batteries is done in three stages: constant current (boost), constant voltage (absorption) and float charge. Different chargers use a range of different voltage set points through these stages to manage this smart charging.
As such we recommend that every three to four months to check and maintain the effective charge state of your batteries. Better quality systems will have a range of protection mechanisms which can be relied upon to allow a quality battery to remain on float charge indefinitely. The recommendation to not leave your charger permanently connected to the battery depends upon individual circumstances but can encourage a proper inspection of the entire power management setup and when combined with allowing the battery to be ‘exercised’ once or twice over a long winter or storage period allows the following.
Check the capacity of your system – is my battery actually holding charge? Maintaining the battery at float charge creates a potentially artificial environment whereby it may appear your battery is fully charged, but when the battery drifts below the float voltage and forces the charger to go back into absorption or trickle charge mode at constant voltage, there is no way to know if your battery is holding capacity. Remember voltage is only an indicator of your batteries potential to supply energy. If your battery is already aged, then this will potentially damage it further. When the charger is removed if the voltage on the battery decreases faster than expected it is likely your battery is on the way out. Better to know this well before you are about to leave on the next trip.
Check the system is safe – a visual check to observe corrosion, cable integrity, browning of terminals (increased resistance due to poor connections), battery has not vented and has maintained its structural integrity. If in doubt check with a suitable qualified auto electrician.
Allowing the battery to be placed under load down to 75-80 per cent of its capacity enables you to see the charger or power management systems is operating effectively. If something has malfunctioned, then the battery may have been accidently allowed to enter into a discharged condition which leads to battery sulphation and there a shorter life span.
Temperature also has a big effect on appropriate charging and the capacity of your battery. Most power management systems and chargers do not allow for temperature compensation. Some may at the actual charger, however, don’t measure the temperature of the actual battery. Batteries heat up during charging and if compensation for this is not allowed for, over-charging can occur. Higher temperature increases the ageing of a battery. At higher temperatures it is well proven that the life of a battery is greatly reduced. Charging and discharging your battery does not help prevent this but something to be aware of as your battery ages.
In summary Jeff, your charger may well be capable of maintaining your battery setup at float charge for an extended period and therefore the advice may not be relevant to your circumstances, however there is no extended harm to your battery in letting allowing it to drop back in charge level to 75-80 per cent of its capacity to check on the aforementioned and maximize the battery life.