Has anyone got some advice on keeping twin batteries charged while in storage. Would like to buy a charger that I'm told just slowly keeps batteries charged up by trickle charging as the batteries start to lose their charge. As my boat is in storage quite away from my home I can't just go and turn on and off as it's needed. Would really appreciate some advice on this, thanks

I think a mod will move the thread.. better than having a double post.
 OK it is not good practice to charge 2 batteries that are different at the same time.. things like cell balance/ resistance kinda stuff.
 In reality if similar ratings same type eg lead acid and not say ld cad  or what ever.. long term will be ok.. but not good practice.
 I have used solar units for yrs..
 The little cheapo $35 (??) from supercheap.. but pull apart and seal with good silcone if going to be in the weather.
 That price would go 0ne for each battery.
 No need for charging modules cause the out put is not high enougn to over come and destroy battery cells

 Get into the bigger 10w units need a module for charging batteries.. and make sure the module Volt out put is for your type of battery

I do not know if can have say 1 10w or bigger solar panel the hook 2 modules in to charge 2 different batteries..
 But this route cost more any way.. getting well over $100
 as to 2x $35 elcheapo .. and mine lasted from early 90s thru to about 3 or 4yrs ago. Included  keeping charged batteries on family camping trips etc.

What BH said above ^^ all sensible.

I have a Ctek M200 ( 25 amp) charger connected  to my BEP switch panel, You can either charge through the VSR or parrallel tha batteries and leave it on.  The M200 is waterproof and perfectly happy charging and monitoring the batteries without any need for me to check them.