We would say that maybe you should think about disconnecting Solar Panels during Summer inactivity as there is growing evidence that batteries are being overcharged when not in long term use?
The damage/benefit depends on many factors from the batteries you use (their age, condition and technology), the Solar regulator and the Power distribution unit, etc.
Victron Energy have published a document that suggests batteries on Boats and Motorhomes are being prematurely aged when a long term 'charging' voltage is applied, when a 'maintenance' voltage would be more appropriate.
First of all can we explain what we think is the difference between charging a battery and maintaining a battery?
When you charge the Habitation area battery, and this applies to almost all Motorhome chargers, the requirement is to raise that batteries charge state.
When you 'maintain' a battery the requirement is to literally put in only what is being lost, no more, no less.
Motorhome Batteries are not designed to be permanently on charge. A modern quality battery, I don't mean a budget 'Leisure' battery, can hold it's charge for 6 months plus. That is a tiny, tiny drain and very different to batteries of 10 years ago when many of these charger units were conceived.
Therefore logic suggests that with such a quality modern battery, to put in any more power than the smallest amount, is going to lead to some measure of excess charging. That excess charging may be very small, or quite large depending on the factors above.
The majority of Motorhome Mains chargers and Solar regulators do not 'switch off' when a battery is up to charge, but drop down into a lower charging state, usually from say 14.4v to 13.8v. They are always charging the battery, albeit at a low rate.
Even when the battery does not want/need any charge they get some regardless.
The Victron Energy document suggests that a 13.8v maintenance voltage is too high, proposing 13.2v is a more ideal. Better still, says the document, remove all maintenance charge completely for a week or so then bring back up to full charge using a 'proper Charge' voltage, like 14.4v.
Other battery manufacturers, after seeing an increasing number of 'Dry' batteries, are suggesting the same.
In the Classic car world, cherished Cars stay wrapped up in the Garage from October to April. It has become common knowledge amongst these owners that leaving a battery on a 'charger' over Winter shortens it's life dramatically.
Classic car Folklore says to use a specialist battery maintainer, like the Optimate, that spends a lot of it's time 'inactive'. The Optimate 'maintains' at a low 13.2v, not the 13.8v of most Solar regulators. It actually switches off, yes physically drops any sort of charge, for half the time it is in maintenance mode.
To additionally support this emerging evidence, the new 2016 Schaudt Solar regulator ( LRM1218 AGM optimised version) has a maintenance voltage of just 13.4v when all previous Schaudt chargers have been around 13.8v. Not quite the 13.2v recommended by Victron Energy, but certainly a change from the norm.
Rumours suggest that from mid 2016 the lesser LR1218 Solar Reg will adopt a 13.2v maintenance voltage. We would suggest you will start to see other charger manufacturers following suit, both mains chargers and Solar chargers?
Therefore, if your battery is a little bit tired, so actually running down more than average, it's life may be extended by being left on charge, but keep an eye on that Acid Level.
Likewise if the battery bank is very large or there is the drain of an Alarm, leaving it on Solar might not do any harm, so long as the Solar Regulator does have very good charge control. Some don't.
Your battery might prefer some disconnection, if the charger :
a). has a higher maintenance output than 13.2v.
b). the battery is a very high efficiency unit.
c). the battery is 'Open Top' like some of the Banner 'wet' range,
We have found the Banner Energy Bull 'wet' acid range particularly prone to fluid loss when left on long term maintenance charge. Likewise the budget 'Leisure' batteries.
See the full text of the Victron energy document here : http://www.aandncaravanservices.co.uk/ehu-full-time-yes-or-no.php
The web page is primarily about long term EHU connection, but the same principal applies.
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