Re: battery experts?
that's just it, I'd like ot have them ready when needed without bringing them inside. I can never get more then a year out of motorcycle batteries.
Certainly outdoor temps will affect the life of the battery - cold affects the chemical reaction going on, and the battery is not able to deliver as much energy. Heat is bad for evaporating the water, which increases the concentration of the acid - and the water is needed to allow the ions to move - so the battery also can't deliver as much energy. If you get very low on liquid, and your plates get exposed to air - they oxygen gets involved... By impacting the chemistry of the battery, they also impact the charge condition of the battery.
Storing a battery while discharged is very very bad for the battery. When charged, the chemistry of the battery is such that things are in a equilibrium of sorts. When discharged, the chemistry of the battery is such that the lead plates are attacked by the sulphuric acid. Leave it discharged enough, and your plates are shot (surprisingly quickly).
Lead/Acid batteries will also loose their charge over time. Depending on the specifics of the battery plates, this can be very slowly or rather quickly.
Deep cycle batteries are made with thicker plates than "SLA" (Start/Light/Accessory) batteries - the common batteries in cars/motorcycles. This is because of how much discharge a deep cycle battery is expected to take (up to 80% discharge), as opposed to a regular car/motorcycle battery (10% discharge).
The regular car battery is designed to deliver a lot of power in a short time frame (ie: starting your car), after which point your power comes from the alternator. To do this, it has been designed to allow as much surface contact between the lead and the acid - eg: thinner plates..
Deep cycle batteries (for the same physical sized battery) do not deliver as much up front 'umph' as the SLA type battery. They are designed with a different intent, ie: to run things from for a while..
It's similar to burning a piece of wood. If you take the wood and split it into thin pieces and put it on a fire, it will burn bright and hot. The same piece of wood split into thick pieces will not burn as bright nor as hot, but will burn longer. That's similar to what's going on with the lead plates in the different battery types. (Although, hopefully, they don't burn... )