A philisophical question

[Grench]

The background info...
I have two Optima D31a batteries in my 80. They're the same age (new), and esentially unused. I have a full amperage 1/2/parallel switching setup. In parallel mode there is a theoretical capacity to supply up to ~2200 CA.

The disadvantage to running with the system in parallel is that I could, in theory, if I left the dome light on, for a couple of weeks, drain them both.

If hey were of different size/capacity or age, a different problem of one battery continually trying to drain the other would be an issue. Since they're both new and identical, this isn't as big of a deal.

The advantage to running the system in parallel is they both stay charged and both retain the same age/capacity.

This isn't a batery isolator kit, it is a true full amperage manual switching system. The 200amp cross system limits seemed just too wimpy to me. If there is interest, I'll do a write-up on my setup. Its pretty much an crude design with a 10x overbuild ratio. OO cables are a b$#ch to work with.

The philisophical question...
So, should I run in parallel, or should I run off of one battery at a time and throw the switch from one to the other every week or so to keep them 'aged' the same?

 

[pulse98]

My opinion:

When the engine is running:
Have both switched on in parallel so they both charge.

When the engine is shut off:
One of them should be disconnected, hopefully automatically. When you run accessories, the starter battery will be disconnected, so you don't deplete it. Then every other month or so, you can switch the one that gets disconnected at shutdown to keep them balanced.

Extra batteries are good for backup if your main battery goes dead. It is also good for extra capacity for accessories when the engine is off, so you don't drain your starter battery.

However, when the engine is running, each extra battery that you add represents an additional drain on the alternator and load to the engine, thus less and less alternator current will be available to the accessories.

 

[Hants]

If you're NOT running an inverter or winch (or other high-amp load), and you ARE running parallel all the time, you shouldn't see more than 80 amps on the line between the batteries.

Starter = 2000W = 157A = Approx 160A MAX, because both batteries are equally (and almost always fully) charged, 1/2 of that would come from each.

A Winch or Inverter changes this dynamic quite a bit. A fridge or ham radio or other non-trivial draw that runs while the engine is off makes it more important to be more sophisticated with your isolation/parallel solution.

There is lots of information on theory & implementation of isolation/parallel/switching solutions in the FAQ (and search).

HTH

 

[decavo]

would you post a pic of where you put the 2nd battery
thanks decavo

 

[Rich]

Since you have already installed the battery switch, it is very simple to add an additional combining solenoid. You can normally run with the battery switch set to an individual battery, and automatically keep both charged. Using the battery switch you can occasionally alternate which battery is primary, and which is backup.

 

[tech_dog]

That's what I've got... a mechanical switch in parallell with an automatic solenoid. So far, so good, and it gives you a lot of options on how you use the batteries.

 

[Grench]

See https://forum.ih8mud.com/showthread.php?t=104630 thread for the install write-up and pics.

 

[wussyPup]

So, should I run in parallel, or should I run off of one battery at a time and throw the switch from one to the other every week or so to keep them 'aged' the same?

For normal day to day use, and always when running, I'd leave them in parallel.
When not used for a long while, I'd leave the switch in the off position; I wouldn't care if the clock and stereo lost their settings, and don't have an alarm.
When camping or other periods with drain and not running; I'd switch to battery 1 (switch to battery 2 for starting, and then switch to parallel when running); I'd always use the same battery for "camping" expecting that it may not last as long as the other, but the "starting" battery will always be in top condition.

So, you only have to change the switch setting when you're doing something special: storage, camping, or first start after camping.

I recently forgot to switch from parallel to 1 on my friend's the boat and the cooler drained both batteries over night. It took a couple hours on the kicker to charge them up enough to start the main motor. (oh, we picked up a 23lb and a 28lb salmon that morning )

Too bad the 80s don't have a hand crank starter like my FJ55 had...

-Steve