I got a nice e-mail this morning from Jim Wagner at Mil Batteries. I want to share it, for folks wanting to purchase new batteries as I do. I think it is very informative and gives you a nice platform to start with...
" The Red Top is a pure engine starting battery. The Yellow Top is a combo starter/deep cycle battery. With the Yellow top you lose a little cranking power but it's a bit more abuse tolerant (leaving the lights on, low alternator output, etc). I prefer the Yellow for most applications. Any of the group 34 size models work with the adapter. In the Red Top that is the model 34 (top post only) or 34/78 (top post and side GMC type terminals).In the Yellow Top it's the D34 or D34/78. The models without the side posts may be a little easier to install.
FYI - Your CCA's don't double with a series connection. Only the battery voltage does. So 2 Yellow Top group 34's will have a pack CCA of 750. The most critical factor in getting a long battery life is charging, charging, charging.
Ideally your alternator should be set so it has a voltage (measured at the batteries) of 28.6 to 29.0 volts. Amperage output should be enough to support all loads. The other factor with vehicles that are not driven on a regular basis or not driven very far is to:
1. have a good charger, designed for sealed AGM batteries. (Optimas are NOT gel batteries. Gel chargers have a voltage setting that is too low. Many conventional battery chargers allow the voltage to go too high for sealed batteries).
2. use a charger about every 3 months to top off the batteries.
I suggest looking at the Interacter products.
www.interacter.com. They have a program setting specific for the Optima battery.
I'd recommend a charger with at least 5 amps. You could also use one of their 24 chargers and wire a NATO plug on it which would make battery charging very easy (you still want to open the battery box to allow air circulation). "