Best Solution For Batteries When Your Caravan Is In Storage

It is always important to look after your caravan whilst it is in storage to maximise the life of your investment.

Question:  I have two 120Ah AGM batteries in my caravan that are currently not in use. I recharge the batteries through a Ctek 15A charger by running a 240V lead from the house approximately once per month. My question is double-edged: 

Is it better for the batteries to be continuously connected to a recharging source than topped up once a month? And if I were to charge them via my Projecta 25A DC/DC charger continuously through a solar panel, what size panel should I purchase? (from Paul Manton)

Answer (David Bayliss): Thanks for the question, Paul. Of course, it is always important to get this right to ensure you maximise the life of your investment in the batteries whilst your caravan is in storage. Mismanagement of lead-acid batteries during this downtime can majorly diminish their capacity—it's not a simple matter of 'set and forget' during an extended period of storage of between 2 and 6 months!

Many will argue that simply leaving your batteries connected to a charger with a 'float' mode will keep the batteries fully maintained and ready for use.  To an extent, this is true, but there is also the possibility of gradual degradation of the batteries if kept in this state constantly. Lead acid batteries contain lead plates surrounded by a liquid or electrolyte solution of diluted sulphuric acid, and as the battery charges and discharges, a chemical reaction occurs between the sulphuric acid in the electrolyte and the lead plates. 

The batteries are designed to be charged and recharged regularly, so having them in a float charge mode at a constant voltage (normally between 12.2-13.4V) can cause them to become 'dehydrated.' When a battery enters this dehydrated state, the level of electrolyte recedes below the level of the top of the lead plates. This would cause irreparable damage to the plates, therefore damaging the battery extensively.

In sum, you are currently maintaining your battery in an ideal way. Undoubtedly you are already doing this, but do ensure natural battery drain – open circuit – or a noticeably light load so as to not inadvertently over-discharge whilst your caravan is being stored. 

To clarify regarding your question on the solar panels, if you are stating that you would like to use these panels during storage, the above advice refers to charging from not only AC power but also DC input power such as solar. The DC power applied through different charging stages to your batteries is the most important thing. If you were to use solar, the batteries would undergo a miniature discharge and recharge nightly as the sun disappears, causing the battery to drop voltage overnight. It would then recommence recharging when the sun reappears the following day. This would occur even throughout winter. However, I would still recommend open-circuiting your battery and leaving it for 2 to 4 weeks before putting the solar panels on.  

In both scenarios, you could use an electronic timer for AC or DC power to let the battery drain and only come back on for, say, two days every three weeks. This would also save having to remember every month!

Overall, I would suggest installing 450W solar panels—space permitting—as this would enable you to charge your panels while on the move and enable off-grid camping. I would also set up a battery-operated DC timer or simply switch off the panels for a few weeks at a time yourself for the duration of your caravan storage period. Best of both worlds! Safe travels. 

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Find your dream van online at OnlyVans.com.au! If this guide to storing and maintaining your caravan batteries has inspired you to take the next steps toward a purchase, we've got you covered.

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This article was written by David Bayliss, with photos by Malcolm Street, and previously appeared at TradeRVs.com.au, now powered by OnlyVans.com.au.  

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