>All the over the road truck I have seen had 3 or 4 batteries in parallel.
>As one several month old battery would fail, only one would be replaced,
>not all.  Usually they broke due to a plate breaking off and shorting out
>the one battery. While trucks do spend a lot of their time running
>(charging), many of them sit (i.e. new on the lot for months on end) and
>there are no troubles with that.

No, actually, the life of the batteries will be shorter. Yes, they will
start the truck for a time, but I will bet you my van that they do not get
the expected life out of the batteries under those circumstances. I will
also bet you my house, that at least one person here will reply that "oh
yes they do"

I assume that you have some empirical data on the expected life of those
batteries as opposed to just guessing that they last as long as they are
supposed to?

>I also hooked two batteries in parallel on a tired old diesel rabbit to
>help it start. It cranked much faster with the two batteries. It was
>typical use of a car. One new battery, one 3-4 year old battery. No
>problems with that either for the last 4 years of its life.

Everyone knows that using two batteries in parallel will allow a better
start. Ever see anyone jump start a car? What does that have to do with
the original post?

>While there is theoretical merit to each battery draining the other there
>seems to be very little automotive data to back this up.

Well, if you want to try and convince people who know better, I recommend
you actually find, or create, the data to back that up, because I have the
data to back up the fact that the life of the batteries will be shorter if
they are not well matched.

Do not confuse those who do not understand by throwing out ridiculous
comments like this. Someone who doesn't understand batteries asked a
question, and all that comes out of comments like this is confusion.

John