I'm no Auto sparky but I'm in the same boat with toys that don't get enough use especially this time of the year...

It cant do any harm, you mentioned 24/7... Well the panels wont really be running at 100% efficiency for much at all of the days this time of year... Consider cloud cover, sun angles changing and of course the dark period... I see it a good alternative to rig up a panel and swap between your batteries... A 40W panel will be putting in stuff all anyway even running at 100% so rig it up and its a bit of trial and error....

Once I'm more organised ( building house at mo ) I am going to have a panel specifically for batteries that are laying
around getting little use and rotate between them... Have a lead running back into the shed, panel facing north and bats sitting on some rubber so anytime I walk past i'll just swap to the next...

 Think there was a similar post the other day, with a link to an old post about a boat burning with a 240v charger so wouldn't recommend that. Solar sounds like a good option.

No solar panel charging expert but I believe you'd need a regulator of some sort to prevent overcharging.

Biggest killer of cranking batteries is being discharged below 50% for anything more than a short period (say a day or so before recharge). House battery or deep cycle will take more discharge to around 80%.

So as long as they are charged fully when you store them they should be right to leave the batt charger disconnected and just connect it to top up every month or so (mine often sits for up to 3 months isolated and fully charged) I get around 3 years before having to replace which is around the same life as in my car with daily use (I have a single 720c in my boat).

 when u run a regulator between th panel and the batteries the reg will ensure the correct voltage is fed to the panels and will sense if the battery is fully charged and pause charging. Hense it won't overcharge the batteries. Ensure the reg is suitable for the panel as if it's max amperage is lower than the panels peak amperage you will damage the reg. 

Morning Muppet..

Been a while since i've done much with the little 12v stuff, let alone solar too. But if not mistaken with a 40w panel, the max current draw ya will get (assuming your open circuit voltage is say, 20volts) would be right on 2 amps. If the panels open circuit rating is 15vdc the max current would be 2.6a.  This  in mind, your batteries are what determines your current draw, yet the limitations are set by the panel. Once my new shed is built for the boat, ill be putting a little panel on the roof and running thru a regulator. The benafits for the reg are to isolate the panel from the batteries if the charging voltage drops below a certain setpoint, which would screw ya batteries. I think a lot of them also have an over voltage protection method, that ensures if the panel cracks the $$%& and your voltage increases too high, it will also isolate it, thus saving your batteries.

What type of battereies are they??

What is the voltage rating's of ya panel?

With the panels, keep in mind that the max current output will only be achievable when the sun is at the perfect angle, the panel in pristine condition and no shadow effects.

 The best and only sure way to keep battery in good nick is to use a very small say 500mA (0.5A) trickle charger/conditioner. The better quality ones will cycle the batterys and keep them in good nick. I'm sure you may be able to find a solar regulator that will do a simmilar job but I have not seen them. But you will need a regulator or you may do the batteries mor harm than good directly connected to the panel.

 After alot of research on this subject, i found this to be the best solution. smartercharger.com/products/dcdc/ctek-d250s-dual/ All in one ,easy to install and gives you multible options. Check out the specs for voltage drop etc. 

I use this with a cteck charger,that i leave hooked on at all times when the boat is in storage ( the last 3 years cause im still working on the boat lol ) I have a had my 200ah deep cycle battery since 2008 and still runs every thing (including my Engel) for many days before i need a re charge. If i am hooked up to the solar panel my battery time is almost limitless.

Most cteck products are weatherproof and designed to be connected permantely. I am not an expert tho, but just saying what has worked for me without a problem . 

Ended up putting 2 x 20w panels with regulators on them. Went to tip, got a foxtel dish bracket, coat of primer/hammertone paint, made a bracket for panels to sit in and covered up back with silicone/ sheet of PVC. One to each battery. Stays hooked up all the time. Went down the track of battery charger etc a few times, got sick of power cord in rain / changing from battery to battery. . Works for me. Def need regulators . Regulators keep current down so they don't boil battery, also they stop reverse charge going out of battery at night.

Was at Whitworths yesterday and they had 20w panels for about $50 each ...not sure of regulators etc on them. Check their website. A couple pics of my set up...

http://www.fishwrecked.com/image/tid/58

https://www.whitworths.com.au/main_itemdetail.asp?item=80021&search123=solar+&intAbsolutePage=1

I used to use the little trickle panels sitting on the back baitboard before that you can get from auto stores too and they kept charge up.

guys for the info and pics.

think i will get inventive like happy.

cheers 

 Picked up a nice 20w solar panel with regulator, alligator clips, lighter socket etc for $84 on special from repco. Whole unit folds away when not in use.

When you lads are talking about the Regulator are you talking about an additional reg to the one that usually comes with a panel or just the panel reg itself?

The panel I have from Ebay the reg shit itself while away camping so that was a hassle especially coz the genni pull cord also decided to shit the tin, anyway got home an bought a newy on ebay and they are cheap and nasty the ones that come on the cheap panels, I recommend getting on ebay and spending the $10 and keeping a spare...

These are the panels I purchased (has the regulator). Good seller, had a question and he answered it straight away and product was good too. I assume link will work . Otherwise if not he is in QLD and called agwholesalers .

http://m.ebay.com.au/itm?itemId=251490817966

Muppet

Happy to help if you need some info. Have gone through this with camping solar panel for camping with lights/engel/4WD etc.. did a fair amount of research...also checked everything via multimeters etc.If you are floating around Carine area more than happy to show/help.