Battery charging

[wranglerin]

I asked this on reddit and couldn't get an answer. For the Wranglers with two batteries - when the battery goes "dead" and the car won't start, and you jump start it with jump leads or a little booster pack, etc, does the main battery power the auxiliary back up or does the auxiliary power the main, or do you have to jump start both??

Sponsored

 

[garyji]

Just Jump the Main. However . . . If you are having to Jump the Jeep, replace both batteries ASAP.

G.

 

[wranglerin]

Just Jump the Main. However . . . If you are having to Jump the Jeep, replace both batteries ASAP.

G.

Thanks, appreciated! It's a good battery I just had a friend accidentally leave the mirror light on for about an hour without my noticing. Not a single other car about so had to call out assistance...thinking of getting one of those portable battery starters.

 

[Fudster]

I asked this on reddit and couldn't get an answer. For the Wranglers with two batteries - when the battery goes "dead" and the car won't start, and you jump start it with jump leads or a little booster pack, etc, does the main battery power the auxiliary back up or does the auxiliary power the main, or do you have to jump start both??

In your JL the batteries are hooked up in parallel, meaning a cable connects the positive terminals on both batteries, and a separate cable, which doesn't interface with the first, is connected to the two negative posts on the two batteries.

The batteries are always, from the factory, in parallel but for an instant before you crank, where the smaller ESS/Aux battery is isolated to test it, and during ESS events when that ESS battery runs your appliances while the engine is off at a stop light and the main batter sits idle, ready to bear most of the effort to crank the engine when the ESS event is over.

Batteries hooked up in parallel should, as the case here, be the same voltage. That voltage will effectively remain constant but the amp hours of the two batteries, at least in theory, will be added to together. If you were to take a voltmeter to the main battery that voltage would represent a composite of both batteries.

Placing your jump cables on the terminals of the main battery charges both batteries because of this parallel connection. Think of the jumper's power going out to both batteries. Purists might argue that the main battery gets the charge first, given its proximity to the jump starter, and I believe because the smaller battery has a greater level of resistance.

But this is all wildly academic. In the real world Stellantis wants you to have the jumper energized cables sitting on the main battery for a while so as to charge the ESS Aux battery. Back in 2018, the original JLs would not even attempt a crank if the ESS/Aux battery was dead. A software patch, downloadable into the early 2018's by the dealer, and built into the later 2018 production run and all dual battery JLs thereafter will still not crank if the ESS/Aux battery is dead, but----a second attempt by the operator to crank should happen only against the main battery. If it successful, the vehicle will take the ESS battery out of the electrical connections of the vehicle until the next cold crank (i.e. where you push the button, not a post ESS event) where an energized ESS battery is detected, and put an "ESS off" light up in the dash, turning off the possibility that ESS will engage, as the battery designed to run appliances during ESS events is dead.

"The battery goes dead" you write. From a dome light left on...? That would eat away at both battery's charge. Or is it that with time one or more of your batteries, likely the ESS one, has gone bad.

If the latter, it is recommended that both batteries be replaced. A load test against each battery, disconnected from the other will determine if a battery has gone bad.

If the former, put your jumper cables on the main battery and let things sit for while to charge both batteries.

Putting a load tester on the terminals of the main battery while all the wires are connected would be a composite load test of both batteries from which no conclusions on either battery could be made.

 

[wranglerin]

In your JL the batteries are hooked up in parallel, meaning a cable connects the positive terminals on both batteries, and a separate cable, which doesn't interface with the first, is connected to the two negative posts on the two batteries.

The batteries are always, from the factory, in parallel but for an instant before you crank, where the smaller ESS/Aux battery is isolated to test it, and during ESS events when that ESS battery runs your appliances while the engine is off at a stop light and the main batter sits idle, ready to bear most of the effort to crank the engine when the ESS event is over.

Batteries hooked up in parallel should, as the case here, be the same voltage. That voltage will effectively remain constant but the amp hours of the two batteries, at least in theory, will be added to together. If you were to take a voltmeter to the main battery that voltage would represent a composite of both batteries.

Placing your jump cables on the terminals of the main battery charges both batteries because of this parallel connection. Think of the jumper's power going out to both batteries. Purists might argue that the main battery gets the charge first, given its proximity to the jump starter, and I believe because the smaller battery has a greater level of resistance.

But this is all wildly academic. In the real world Stellantis wants you to have the jumper energized cables sitting on the main battery for a while so as to charge the ESS Aux battery. Back in 2018, the original JLs would not even attempt a crank if the ESS/Aux battery was dead. A software patch, downloadable into the early 2018's by the dealer, and built into the later 2018 production run and all dual battery JLs thereafter will still not crank if the ESS/Aux battery is dead, but----a second attempt by the operator to crank should happen only against the main battery. If it successful, the vehicle will take the ESS battery out of the electrical connections of the vehicle until the next cold crank (i.e. where you push the button, not a post ESS event) where an energized ESS battery is detected, and put an "ESS off" light up in the dash, turning off the possibility that ESS will engage, as the battery designed to run appliances during ESS events is dead.

"The battery goes dead" you write. From a dome light left on...? That would eat away at both battery's charge. Or is it that with time one or more of your batteries, likely the ESS one, has gone bad.

If the latter, it is recommended that both batteries be replaced. A load test against each battery, disconnected from the other will determine if a battery has gone bad.

If the former, put your jumper cables on the main battery and let things sit for while to charge both batteries.

Putting a load tester on the terminals of the main battery while all the wires are connected would be a composite load test of both batteries from which no conclusions on either battery could be made.

This is everything I wanted to know and more - thank you SO much. You explain it so simply. I'm new to the Wrangler so I didn't even know there were 2 batteries until a couple months ago... which brought up a whole bunch of questions I couldn't find answers for. Thanks again.

Sponsored