Connecting batteries in parallel

[smallfry]

As title says, I need a battery for my new toy. Originally it had one of those large tractor batteries with the terminals at on end (Can't remember the type number)

However, these are expensive, and as the vehicle will be seldom used, I dont want to leave it installed because.........

A. It will not do it any good in the long term, and it will die prematurely AND its too heavy to carry downhill from where the vehicle will live.

B. We seem to have a fair few of the "metal collectors" round here, and no doubt will soon go missing if left in situ.

So, I thought I could make a new battery tray/box (it needs one anyway) and install two smaller batteries, wired in parallel, which will also suit our diesel vehicles, so they can be more usefully swapped around and used. 

So, I have found information that the AH capacity will be doubled, which of course is fine, but I cant find anything about the cranking amps, so my question is, would I be right in assuming that this would ALSO be doubled ?

Does anyone actually know for sure ?

[FridgeFreezer]

In theory yes, if you parallel two batteries you get double the amps.

Not sure how many cranking amps you feel you need though - the limiting factor will be the thickness of the starter cable even with a single battery. And if you uprate the cable you risk popping starter motors.

[Escape]

2 batteries in parallel should do the trick. You might even find that for a similar size 2 modern batteries give you more Ah and CCA than the big old one.

I would make sure you disconnect the batteries when not used for any amount of time, to avoid stray currents from one to the other than can deplete and damage them. Getting identical batteries will limit this effect, but it might still be there. Maybe fit a switch if you don't plan to take them out every time. Charging in parallel wont be the best solution, but should be fine for normal use. The RRC VM used twin batteries without any fancy charging setup and you don't hear of much problems with those.

Care to elaborate on the new toy now that you've got our attention? 🙂

Filip

[smallfry]

12 hours ago, Escape said:

Care to elaborate on the new toy now that you've got our attention? 🙂

Filip

I didn't say what it was as its NOT a Land Rover.

I went with Brother in Law to look at a large pre enjoyed greenhouse that was for sale that he wanted, and would need dismantling. I only went to see what was involved.

But I came home with this........... It does have a few issues though !

[missingsid]

Sweet

[Escape]

That could prove very useful in dismantling the greenhouse. 🙂

Congrats and I'm sure nobody minds non-LR content when it's this cool!

I wouldn't expect the engine to need that much to turn over, so something like a Defender sized battery (100Ah, 800CCA) should be plenty.

Filip

[L19MUD]

@steve b is the expert on these

[miketomcat]

We regularly fit two smaller battery's wired in parallel or series (depending on application). As said above two new identical battery's treated as a single battery is best or charged and discharged together. I would use the existing cabling or replace with the same section but use a slightly larger section between the two battery's. We normally leave them connected together but isolated from the rest of the boat. Current install is two 50amp blue top optima's wired for 24 volts to start two (one at a time) 6 pot 180hp ford D series mermaid diesels in a fairey super swordsman.

Mike

[smallfry]

19 minutes ago, L19MUD said:

@steve b is the expert on these

Now that might be useful ! 😄

[Blanco]

21 minutes ago, miketomcat said:

two (one at a time) 6 pot 180hp ford D series mermaid diesels in a fairey super swordsman.

... sounds very nice, (as we are appreciating non LR 'toys' 😉)

[smallfry]

1 hour ago, Escape said:

I wouldn't expect the engine to need that much to turn over, so something like a Defender sized battery (100Ah, 800CCA) should be plenty.

Filip

I have sort of come to that conclusion Filip.

By the time I have bought two batteries, extra terminals, isolator, cables etc. I may just as well use a smaller single battery, as I will not be taking it anywhere in sub zero temperatures (Yet) I certainly wouldnt want to take it anywhere in snow as its very top heavy and wallowy because of the crane.

It just so happens that the battery on my old Renault Master is the capacity you quoted !

[miketomcat]

Optima's have very good cold cranking for their size.

@Blanco the swordsman is not mine I work for a company restoring classic powerboats.

Mike