Where to attach battery charger in 2 battery system? - Chevy and GMC Duramax Diesel Forum
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post #1 of 5 (permalink) Old 12-20-2019, 09:16 AM Thread Starter
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Where to attach battery charger in 2 battery system?

2005 LLY Duramax with 2 batteries. Clock keeps resetting itself to 12:00 every time I start the truck and the batteries seemed a little weak on starting. Alternator is putting out 14.4-14.6 volts at idle so I think the batteries are on the way out. I want to connect my charger to see how it reacts.

I thought I should connect the charger (+) clamp to the post inside the red box marked BATTERY (+) just below the GND tab and attach the charger (-) clamp to the GND tab but I got no response from the charger. Is this the wrong way to connect a charger?

Connecting the charger to either battery results in charging so I know the charger is working. With 2 batteries I'm unsure how to proceed to be sure both batteries are charged.

I left the charger on one battery for a little while and, although it looked like it was going to charge normally, after a while the charge needle started jumping up and down. This happened with both batteries which, by the way, are about 5 or 6 years old.

Paul
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post #2 of 5 (permalink) Old 12-20-2019, 09:43 AM
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I would remove the batteries and have them load tested and if one is bad replace them both, that being said you can charge both batteries by hooking the charged to either batteries as the are connected together to perform as one big battery.

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post #3 of 5 (permalink) Old 12-20-2019, 09:59 AM
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Your batts are toast.
Two halves of one large batt, always replace in pairs.


If you're a member, the best deal out there I've found currently for wet Group 78s is this @$103.
800CCA / Free replacement 36mos warranty.
Made in U.S.A.
https://www.samsclub.com/p/duracell-...lp_product_1_1

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post #4 of 5 (permalink) Old 12-20-2019, 11:13 AM
J83
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Quote:
Originally Posted by lpaulcarter View Post
2005 LLY Duramax with 2 batteries. Clock keeps resetting itself to 12:00 every time I start the truck and the batteries seemed a little weak on starting. Alternator is putting out 14.4-14.6 volts at idle so I think the batteries are on the way out. I want to connect my charger to see how it reacts.

I thought I should connect the charger (+) clamp to the post inside the red box marked BATTERY (+) just below the GND tab and attach the charger (-) clamp to the GND tab but I got no response from the charger. Is this the wrong way to connect a charger?

Connecting the charger to either battery results in charging so I know the charger is working. With 2 batteries I'm unsure how to proceed to be sure both batteries are charged.

I left the charger on one battery for a little while and, although it looked like it was going to charge normally, after a while the charge needle started jumping up and down. This happened with both batteries which, by the way, are about 5 or 6 years old.

the batteries are connected in parallel, basically making them 1 large 12V battery. Just connect the charger to where ever is convenient, be it either battery or the jump box, and your good.

Edit, finished reading the post, you probably need new batteries, but you they are still wired in parallel for charging.

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post #5 of 5 (permalink) Old 12-20-2019, 11:16 AM Thread Starter
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Thanks all. Batts were dead, already replaced them and all is good. Resolved the GND tab issue too: just a poor contact between two parts of the bracket.

Paul
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