I just bought my first diesel and couldn't find the answer to my question in the owner's manual.. so what's the purpose of the 2 batteries? Is one to start the engine and the other to power the glow plugs? Or are they both wired in parallel?

both wired in parallel. Between the high compression of the engine, glow plugs, and intake air heater, diesel engines need lots of current at start up. That's why you have two batteries.

It's for your ipod ):h

Sorry couldn't resist. Diesels take a lot of juice to turn over. Especially in the winter with the heaters and everything drawing power as well. Just as sowilson said, they are in parallel. Which still gives you 12 volts but doubles the capacity.

Come on guys...thats not it at all! It so when you pop your hood by your buddies piece of Dodge or flippin Ford, it just looks much cooler!!:cool:

That and the dual alternators.

These fast start glow plugs are current hogs! I've measured peak current >250Amps !into the glow plugs, and 250+ amps drawn by the starter on a warm day. all this means dual batteries. When it's cold (32F) I'll bet current goes even higher.

Plus it always helps to have two batteries so you can power your aftermarket accesories whatever they may be.

Does anyone know what the load is that draws on the battery for a few minutes after battery is reconnected, I was testing for a load before I replaced the battery and found a significant load for a few min. then it completely went away, I figure some kind of capaciter.

was the key in it? Sounds like a glow plug, or grid heater.