Trickle charge'n

[Mr._Bill]

The AUX/ESS battery is there to maintain stability for all the computers and electronics the vehicle contains. They tend to malfunction when the voltage drops too low. It also allows battery changes without dropping power and rebooting everything. I left the factory system intact and added a smart Isolator and a third battery to power the winch and lights.

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[u-joint]

Someone please correct me if I'm wrong, but if I'm following this disucssion correct then it is safe to use a NOCO genius charger on the JT. Simply connect it to the primary battery as usual, and since the two batteries are wired in parallel the charger will "do the right thing".

Sound about right?

 

[Radio Guy]

I would question why you couldn't use a high current charger. If the alternator is connected to both batteries during normal operation, that could provide a lot of charging current to both batteries simultaneously.

@u-joint

Yes, using a battery tender / maintainer as you state, hooked up to the Main batteries pos and neg, will see both the Main and Aux battery being tended to / maintained. Just do not hook up a full blown (high amp output) battery charger to your JT like this...

Best bet is to go with a low amp output battery tender / maintainer that puts out say 1, 2, 5 amps.

 

[Mr._Bill]

I would question why you couldn't use a high current charger. If the alternator is connected to both batteries during normal operation, that could provide a lot of charging current to both batteries simultaneously.

The truck is supposed to be equipped with a 'smart' charging system that gives priority to the main battery. It would need some ability to control charging levels to keep from cooking the lower capacity ESS battery.

 

[ShadowsPapa]

I would question why you couldn't use a high current charger. If the alternator is connected to both batteries during normal operation, that could provide a lot of charging current to both batteries simultaneously.

Well, think about what's happening when you jump a dead Jeep - the vehicle providing the starting power is running and likely has a system voltage of 14 volts or so, depending on the regulated voltage. So we know for short term, it's fine plus the voltage is limited by the regulation of the vehicle doing the jumping. It's not going to exceed what a typical battery can handle, and you are doing it short term. (not likely to make either battery "hot")

Charging batteries is a matter of supplying enough voltage to charge the battery technology being charged. Some require more "push" or higher voltage, to get the job done.
Two unlike batteries can mean that the load of one battery causes the charger to run at a higher voltage than the other battery needs or can handle.
When using an outside charger (not the alternator) that has capability of higher voltage (which is how they push the higher amperage, you do want to make sure you aren't doing a "fast charge" as that means you are pushing some pretty high voltages to a battery technology that may not handle it.

 

[Radio Guy]

From the diagrams I've seen the two batteries are in parallel at all times except when the engine is shut off during an Electronic Start Stop event. That means if both batteries are low and in serious need of charging they will both pull lots of current from the alternator if its spinning fast enough to deliver rated current. Same will happen if you jump start the Jeep, both batteries are in parallel and will hog a bunch of current.

However, with a given charge voltage, lets use 14.0 volts in this case, the smaller battery will draw an appropriate but much smaller amount of current compared to the larger battery as they are in a charging phase. Both batteries will charge at different rates and achieve full charge state at different times due their mismatched capacity.

This is why I questioned why you could not use a higher charge rate over a maintaining/tending type charge and I'm not specifically speaking of those giant wheeled chargers that can put 16 or 18 volts across your battery for a mega fast charge, just the usual 14.2 nominal volts which is the typical fast charge rate for lead acid types. The answer is you can within reason and it happens every day as you drive the vehicle.

The truck is supposed to be equipped with a 'smart' charging system that gives priority to the main battery. It would need some ability to control charging levels to keep from cooking the lower capacity ESS battery.

 

[jebiruph]

The truck is supposed to be equipped with a 'smart' charging system that gives priority to the main battery. It would need some ability to control charging levels to keep from cooking the lower capacity ESS battery.

The alternator connects to the high capacity fuses that feed both batteries. There aren't any electronics that prioritize the charging order of the batteries, but the longer cables/higher resistance to the aux battery will impact it's charging rate.

There is a battery sensor on the main battery that impacts alternator output, but the same alternator output still goes to both batteries.

 

[BlueCT]

I know this is an old thread but I went to charge my main battery with a Noco genius charger and went down a very long rabbit hole regrading ESS and the aux battery. Long story short in my JT the main battery is an AGM battery. These are kind of uncommon but becoming more common as they are better for start stop function. The Noco has a specific mode for AGM batteries. So to answer the question and help others in the future yes you can charge the better but you should look under the battery cover to see if it is an AGM and used that mode on the charger.

 

[ShadowsPapa]

I know this is an old thread but I went to charge my main battery with a Noco genius charger and went down a very long rabbit hole regrading ESS and the aux battery. Long story short in my JT the main battery is an AGM battery. These are kind of uncommon but becoming more common as they are better for start stop function. The Noco has a specific mode for AGM batteries. So to answer the question and help others in the future yes you can charge the better but you should look under the battery cover to see if it is an AGM and used that mode on the charger.

These are all AGM batteries, from day 1.

Both crank and aux are AGM.

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