by Logan_Walthers » Thu Jun 22, 2017 8:38 pm
Doug,
In my experience, I would never let a cell sit for any extended period of time at 1.225, as that is right about the limit where the plates of the battery start to sulfate, which will kill the capacity of your battery. It's really dependent on how 'deep' you are cycling the batteries regularly. That is, if you're using 80% of the available capacity regularly, keeping the SG a little lower will stretch the life of the battery. I usually shoot for around a 1.265, which tends to be the sweet spot. Generally, you compensate for temperature by adding .001 for every 3 Degrees above 25C and vice versa.
Specific Gravity is kind of a tricky thing. The general rule is that Deep Cycle Batteries should be kept a bit higher than Float batteries, but there are tradeoffs.
High SG gives you good impulse-current response and better capacity, but is more corrosive, so your battery will degrade quicker if it's too high.
Low SG is just the opposite, you take a hit on impulse-response, but get more cycle life from the battery, and if it's too low, you will start to build sulfation on your plates .
Deep-cycle batteries are made with very thick plates that can handle being cycled to very low State-of-Charge (though I would try not to go lower than 20% SoC, as that will kill any battery quick). The float type have much thinner plates, to maximize surface area and have better ability to handle any large transient current draw.
Hope that helps. If you've got any questions let me know.