Chanrging Parallel Batterys

Went to start the 966 since if finally got above 30 degrees so I can get the #1 fuel through the system, and batteries are dead.
I have it wired with 2 12v batteries in parallel. + to +
Should I put the charger on the 1st battery, or on the second battery that goes to the starter. My thinking is the first battery

Thanks

As long as they are hooked together the weaker one will draw more from the charger.

Hello rustyacres,

Theya are together right? Just put the charger on.......

Guido.

It shouldn't matter if your connections are good and the batteries are good. But why are they dead? It might be a good idea to disconnect them so you can troubleshoot the problem if it's not obvious. You could charge them together and then separate them for testing, check them with a voltmeter and then crank the engine with each battery separate, (with the voltmeter on the battery) that's a good way to load test a battery. You will probably get a lot of varied opinions, some good, some not so! This subject has been beat to death lately, it's that time of year!

I agree. My first test would be to disconnect them and walk away for an hour then get a rest voltage on each independent from the other. If different (and the batteries are the same) I would try charging the weaker one with more than 10 amps for 2 hours (or automatic) to see if it can be equalized. Either way if one is mediocre, replacing both and using the good one on the farm truck might be reasonable. Jim.

Hook it up just like you would if it only had one battery. You will be charging them both at the same time so which ever battery is the weaker one is how much you will charge the other one.

Hook your charger to the + terminal/bat lead, on the starter solonoid and the neg of your charger to a good ground near the starter.
Loren

First of all be aware if two are connected in parallel and one is bad it can draw off the good one. It's best when two batteries are connected they be IDENTICAL the same age and brand and type and size and rating. Its cheap (free usually) to have a battery shop do a load test to insure you don't have one bad battery sucking down the other, you may want to do that. At least check electrolyte and voltages of both batteries first. A "good" full charged 12 volt battery should read around 12.6 volts once stabilized and at rest.

While it will "work" if the two are connected in parallel, if you simply place the chargers + and - to the + and - of ONLY ONE of the two batteries, ITS MUCH BETTER IF YOU HOOK THE CHARGERS + TO THE + OF ONE BATTERY AND THE CHARGERS - TO THE - OF THE OTHER BATTERY. Yes Billy Bob and Bubba I know either way still works !!!!!!!!!!!!

If you want to understand why the above is better, read through Smart Gauges research, you may not believe how much difference it can make as far as better balancing for charging and load currents. When us RV owners wire up several RV batteries this becomes more important so they all receive more equal charging and load currents

John T
Parallel Battery Charging

Most batteries should not be connected in parallel when charged but rather disconnected and charged separately.

Dean

Thanks for the enlightenment. The old timers always said to avoid "daisey chains" but I never gave it much thought.

ASSUMING you have two identical or similar batteries of the same age connected in parallel, simply charge the *(*&^ things as they are.

If one is weaker or blah blah blah as some have posted no matter how you charge them it ain't gonna go well.

Bottom line is if you have a diesel tractor and you expect it to start reliably you need to budget some $$$ to keep a good battery or two in it.

(Please don't shoot the messenger!)

I would not worry about separating the batteries, the alternator does not separate them, so why should you.

First off, avoid putting lead/acid batteries in parallel(+ with +, negative with negative). If you need more amp hours, buy a bigger flooded lead acid battery, but keep it all in the same case. There will never be a pair of batts that have the same residual charge, and they will go into sympathetic discharge if left connected.

Next, if you must put them in parallel, use a quick disconnect between the negative terminals, or use one of those marine battery disconnects where you can have 1, 2, both, or off. Leave it off when not in use.

Last, you're working with a lot of amps. The cables need to be big, clean and tight. Any kind of resistance will build up corrosion and get worse.

When I put the second battery in my truck this summer, I installed a disconnect on it so I can quickly disconnect the battery any time the truck is going to sit for any length of time. That way, no sympathetic discharge.