tuga, richard is right.
think of it like a flashlite. when you have an old flashlight with the C or D batteries in it, you put them front to back until you had filled up the chamber, remember? in doing postive to negative, you are adding together the voltages to get a brighter light. more batteries, the brighter light.
however, your starter in your coach is 12v. it needs 12v. however, since it is a HUGE starter, it needs a lot of CURRENT to turn over under the load of the engine. to do that, you need to have lots of cranking amps. amps are additive, so when you hook up in parallel, (positive to positive and negative to negative) you keep the voltage the same and sum the cranking amps up. even my f350 diesel truck has two batteries and when one of them is the least bit low, it wont start. diesels like to be spinning fast to start. remember, our diesels are basically a controlled explosion activiated by fuel and pressure. since they are high pressure in the cylinders, it takes lots of cranking amps to turn it over fast enough to get it started. for me, the fun example that is very illustrative are diesel powered pile drivers. the ones they use to pound bridge supports that are 3 feet in diameter down 100 feet. they set a huge cylinder on top of the support to be pounded in, support it on the outside gently, lift the piston (hammer) up and let it go as they squirt diesel fuel into the cylinder. it explodes, shoots the piston back up and it all starts over again. it is amazing to watch and they control the hammering pressure by how much fuel they squirt in. a simple one cylinder diesel engine that doubles as a hammer.
as to which 8D battery to buy, i have a simple approach....which is cheapest? that may not be the official newell approach, but it is mine.
there are not dozens of makers of 8D batteries and most are just remarked from a few manufacturers.
i bought mine at SAM's club and paid 135 bucks apiece. they are made by interstate and actually have higher cranking amps than the interstate workhorse batteries i replace. i think mine are 1400 CCa. SAM's club has their own interstate label.
can ya tell i took a long nap and now know i will be up all nite so i am writting to much?
as wally says, thats my two cents worth and i am sticking to it.
tom
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