O.K. to charge battery w/o disconnecting cables? - TerrainForum.net: GMC Terrain Forum
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post #1 of 15 (permalink) Old 11-16-2019, 01:50 PM Thread Starter
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O.K. to charge battery w/o disconnecting cables?

2019 terrain denali... We are not using the car much this time of year and I know there's a fair amount of parasitic drain on the battery with it just sitting in the garage.. I'd like to put my smart charger on the battery to top it off but wonder if this is safe to do .. I know there are diodes and circuits that could be damaged if everything is left connected and a high rate of charge is used so I was thinking about charging at just 1 amp ... Would this be o.k. or should I charge at half an amp?.. It's a three stage charger that will automatically go from bulk charging to constant voltage and decreasing amperage phase followed by a float charge.. I can adjust the amps /volts and figured I'd use 13.5 volts as peak voltage ... I could disconnect the battery cables but then I'd lose presets etc. etc.
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post #2 of 15 (permalink) Old 11-16-2019, 03:10 PM
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Check page 342 of your owners manual for vehicle battery storage info etc.

2013 Nox 2.4L 1LT AWD from western PA.
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post #3 of 15 (permalink) Old 11-16-2019, 03:17 PM Thread Starter
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The owners manual gives no specific instructions on charging the battery(at least my manual doesn't), only jump starting instructions.. That's why I'm asking here

Last edited by tic; 11-16-2019 at 03:22 PM.
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post #4 of 15 (permalink) Old 11-16-2019, 04:14 PM
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If the vehicle can be jump started, as per the owners manual; then it can be charged without removing the cables also.

The procedure should include turning off the ignition and any accessories first.

The use of one of the newer smart chargers; ones that have reverse polarity protection would be advisable.

If using a higher amperage output charger, and you only intend to use it for a maintainer; select the lowest output, and when it is charged fully will automatically transition to the float mode which typically maintains ~13.2 volts.

I have a pigtail installed on all of my vehicles that will accept a float mode/maintainer/charger. I don't use my higher amp chargers for this purpose, but you definitely can.

I use the Battery Tender Plus as my maintainer; puts out one and a half amps to charge, then goes into maintenance mode. I have four other off brand float mode maintainers that I occasionally use, but monitor them more frequently as I don't fully trust them.

You may wish to invest in a dedicated maintainer vs using a larger charger if all you wish to do is maintain the battery. Larger chargers often have a fan that operates all the time, and is overkill for using as a maintainer.

If you do ever need to charge a dead battery that's installed in your vehicle; then I would recommend disconnecting the battery cables prior to charging.


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post #5 of 15 (permalink) Old 11-16-2019, 06:16 PM
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If your that worried , use an AGM battery

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post #6 of 15 (permalink) Old 11-16-2019, 06:59 PM
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Originally Posted by bigb12359 View Post
If your that worried , use an AGM battery
The owner's manual indicates that all North American Terrrain's, regardless of trim level, come equiped with an AGM battery.

2018 Terrain Denali, 2.0T, Blue Steel Metalic/Black
2013 ATS Premium, 3.6 V6, White Diamond Tri-coat/Brownstone
1967 Camaro, 327, Butternut Yellow/Black

Last edited by jerrymander; 11-17-2019 at 02:44 AM.
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post #7 of 15 (permalink) Old 11-16-2019, 07:03 PM Thread Starter
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It's not a matter of being "worried" LOL.... the car already has an AGM battery and yes, the self discharge rate of AGM is very low 1-2% per month. With the car sitting for long periods of time w/o use, I'd just like to top it off ocassionally to prevent sulfiation of the plates... I don't know what the parasitic drain on the battery is with the car turned off but I imagine I have a higher discharge rate than one or two percent per month because of stand by drain of various systems... I do have a three phase charger that I can adjust the rate from .1 amps up to 10 amps and set various chemistries and parameters. It's actually pretty small, about the size of a paper back book but does have a fan that will turn on if it gets hot. I was just trying to see if anyone knew of any possible problems with charging the battery with the cables hooked up or what the max charge rate should be to prevent any possible damage to electronics.
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post #8 of 15 (permalink) Old 11-18-2019, 03:20 PM
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Battery Electrical Drain/Parasitic Load Test

12 V Battery
The following procedure is for the 12 V battery only.
Diagnostic Instructions•Perform the Diagnostic System Check - Vehicleprior to using this diagnostic procedure.
•Review Strategy Based Diagnosisfor an overview of the diagnostic approach.
• Diagnostic Procedure Instructionsprovides an overview of each diagnostic category.
Circuit/System Description
Components most likely to cause a parasitic draw on the vehicles battery are switches, relays, and control modules. Afterthe ignition is turned OFF the control modules will begin to go to sleep shut OFF. All control modules do not go to sleepat the same time, some may take up to 30 min or longer after turning the ignition off before going to sleep. Other modulesmay periodically wake up then go back to sleep. These are all normal conditions.
Diagnostic Aids•When diagnosing an intermittent battery draw, if the battery voltage is interrupted by disconnecting the battery, it may causethe condition to clear. You may want to connect the EQPMSK6211 Battery Booster Pack or equivalent to the positive and negativebattery cables prior disconnecting the negative battery cable to prevent a loss of voltage.
•Rule out any possible aftermarket equipment causing an unacceptable parasitic current drain. Aftermarket accessories installedinto the courtesy lamp circuit can cause the inadvertent power timer in the body control module (BCM) to keep resetting. Thismay cause the BCM to remain awake and cause a current drain on the battery.
•Refer to: Checking Aftermarket Accessories.
•Rule out customer driving habits such as regular short trips that do not allow enough time to properly charge the battery.Refer to Battery Description and Operation.
•Verify that the battery and charging system are in proper working order. Refer to Battery Chargingand Charging System Test.
•A battery discharging for no apparent reason while the vehicle is parked can be caused by an intermittent draw, such as amodule waking up, or a continuous draw, such as a dome light or stuck relay.
•An engine off natural vacuum evaporative test can occur if the engine control module (ECM) determines the drive cycle hasmet the appropriate criteria immediately after key off. The ECM will stay awake and the vent solenoid will stay energizedfor as long as 45 min. The typical current draw for this is about 1 A.
•The K9 Body Control Module has discrete input and output terminals to control the vehicle's body functions. The K9 Body ControlModule is wired to the High Speed GMLAN bus, Low Speed GMLAN bus and multiple Local Interconnect Network (LIN) buses and actsas a gateway between them. The various K9 Body Control Module input and output circuits are illustrated in the correspondingfunctional areas on the K9 BodyControl Module electrical schematics.
•The K9 Body Control Module functions as the power mode master. The ignition switch is a low current switch with multiple discreteignition switch signals to the power mode master for determining the power mode that will be sent over the serial data circuitsto the other devices that need this information; the power mode master will activate relays and other direct outputs of thepower mode master as needed. Refer to Power Mode Description and Operationfor a complete description of power mode functions.
•The K9 Body Control Module functions as a gateway or translator. The purpose of the gateway is to translate serial data messagesbetween the High Speed GMLAN bus and the Low Speed GMLAN bus for communication between the various devices. The gateway willinteract with each network according to that network's transmission protocol. All communication between the K9 Body ControlModule and a scan tool is done through theprimary High Speed GMLAN bus.
•Digital OnStar Generation 6 and later vehicle communication interface module do not “wake up” every 10 minutes for the first48 hours as the Generation 5 and prior. Generation 6 and later vehicle communication interface module current draw is verylow, less than 40 mA, so the OnStar system is left in that state for up to the first 48 h. Parasitic draw of up to 40 mA withan occasional spike as high as 80 mA through the vehicle communicationinterface module for the first 48 hours is normal.
•Some automatic climate control systems can remain in a semi awake state for up to three hours, actual draw amounts vary byvehicle platform but are typically not greater than 50 mA.
•An extremely low mA current level is consumed by the body control module for monitoring purposes, actual system wake up onlyoccurs when the fobs for the vehicle are used. When other devices on the same remote keyless entry operating frequency areactivated, such as the 4 tire pressure monitoring sensors and other vehicle Fobs in the vicinity, the body control modulewill have a 100 mA spike. These spikes are normal and occur toobriefly to have a significant effect on battery drain. Competing signals may cause remote keyless entry performance issuessuch as jamming but should not cause excessive battery draw.
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post #9 of 15 (permalink) Old 11-18-2019, 03:21 PM
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•If an excessive current draw is not present during initial testing, continue periodic testing over a 1–2 hour period to seeif the current draw increases and stays above an unacceptable level.

Note: The battery specification listed below is a generic specification. Refer to the label on the original battery when testingthe battery.
•The battery run down time will vary depending on the batteries reserve capacity. If the reserve capacity is higher, then thebattery run down time may be longer. If the reserve capacity is lower, then the battery run down time may be shorter. Thegraph below indicates roughly how many days a 690 cold cranking amperage battery with a 110 min. reserve capacity startingat 80 percent state of charge will last with a constant current drawuntil it reaches 50 percent state of charge. Differences in battery reserve capacity and temperature will affect the results.

Current Drain


25 mA


50 mA


75 mA


100 mA


250 mA


500 mA


750 mA


1 A

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post #10 of 15 (permalink) Old 11-18-2019, 08:44 PM Thread Starter
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Thanks for the detailed information!
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