Dead Battery - Can not get it to start

[mdfilip]

My Bronco was sitting for about 2 weeks and I went out to start it and it's completely dead. I put a charger on it and it was doing all kind of crazy stuff. I disconnected the battery and charged it for about an hour ... hook back up and I get power and same wacky crap flashing on and off and when I try to start it everything dies. I always get notification saying it goes to sleep to preserve power but this is the first time I let it sit this long. Any suggestions?

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[CitrusBronco]

I think the message that it’s going to sleep to preserve power is like an early warning your battery is going bad unless you left an accessory on and it’s a one time thing. Looks like your past that and need a new battery.

 

[joes bronco]

2 things here ,1- don't let your bronco sit that long before starting it, the ecm is active all the time. This situation is happening a lot on several different forums, guys let their vehicles sit for a number of days then drive it a short time, 10-20 min. then let it sit for several days. After they have done this several times the batt runs out of power.

2- Not knowing how you connected your batt. charger, here is the proper way to charge a batt that has a batt. management system. Charger red or positive to the positive batt. post, then negative to a ground point on the vehicle. Do not put the negative clamp on the negative batt post. The charge has to go through the batt management system so your computer can see that the batt. is being charged.

Surprisingly very few people are aware of this, as a retired mechanic I didn't know about it until about a yr. ago

 

[[DELETED MEMBER 27901]]

2 things here ,1- don't let your bronco sit that long before starting it, the ecm is active all the time. This situation is happening a lot on several different forums, guys let their vehicles sit for a number of days then drive it a short time, 10-20 min. then let it sit for several days. After they have done this several times the batt runs out of power.

Mine will go into deep sleep after 5-7 days of not driving. If I went 2 weeks like OP, my battery would definitely be dead.

I keep an 8amp charger on hand will do a complete top up once or twice a year if I know I'm doing a bunch of 10 minute drives in harsh conditions.

 

[joes bronco]

I have 2 rigs, my bronco and a 2017 f150 , the truck sets a lot but I drive it at least once a wk. about 30min. or more, even then the batt. voltage will drop enough that the auto start-stop wont kick in.

The batt. management system drives me nuts though. Because of all the electronics in todays vehicles it's pretty much a must but why can't the manufactures design one that will recognize the batt voltage only then apply that to the electrical system.

In the good old days if your batt. went dead you just charged it up and good to go. With todays vehicles if you charge up a dead batt. using the batt. posts only, the batt. will charge up alright but the batt. management unit won't recognize the batt. is at full charge and so keeps everything shut down, go figure that one out.

 

[mdfilip]

Update.... I left the charger on 10A and got it started. The dealer said it was still under the 3/36000 and will change it if it's bad. After this I will be installing the battery tender that I purchased months ago but have not had the time to install it, I will make time now. As stated above I drive very little because I have a work vehicle and also a Superduty to plow with the bronco sits in the garage and when I do drive it, it gets maybe 15-30 minutes at a time if I'm lucky. Dealer also said these batteries are only good 3-5 year.

 

[mdfilip]

2- Not knowing how you connected your batt. charger, here is the proper way to charge a batt that has a batt. management system. Charger red or positive to the positive batt. post, then negative to a ground point on the vehicle. Do not put the negative clamp on the negative batt post. The charge has to go through the batt management system so your computer can see that the batt. is being charged.

When installing a battery tender should it also be connected to only the positive side of the batter and the negative side to chassis ground?

 

[tobands]

The bronco has an AGM battery and need a charger/starter thats agm compatible... Thats why all the weird flashing

 

[tobands]

When installing a battery tender should it also be connected to only the positive side of the batter and the negative side to chassis ground?

i always ground to the chassis

 

[B22-2023]

Right. @Ducati1098 has said recently and many times - chassis ground so you don’t mess up the BMS logic.

 

[Ducati1098]

Battery Charging
Charging

NOTE: Batteries will discharge due to normal parasitic key off-loads when the vehicle is on a dealer lot or parked by the customer for an extended period of time. Vehicles still in dealer inventory or in long-term storage may be driven short distances with heavy electrical loads. Over a period of time (30 days or more), this could result in vehicles having shallow or deeply discharged batteries.

NOTE: The vehicle charging system is designed to supply the electrical power needed to maintain the battery near full charge during normal vehicle use. The charging system is not capable of bringing a deeply discharged battery back to near full charge in a short amount of time such as allowing the vehicle to idle for 15 minutes to recharge the battery. Use an external charger to charge discharged batteries.

NOTE: Cold batteries will not readily accept a charge. Allow batteries to warm to approximately 5°C (41°F) before charging. This may require 4 to 8 hours at room temperature.

Charger Connected to Engine or Chassis Ground - Preferred Method

NOTICE: Do not connect the negative (black) charger clamp directly to the battery monitoring sensor, it must be connected to an engine or chassis ground to relearn the battery's state of charge.

1. Connect the positive (red) charger clamp to the positive battery post.

2. Connect the negative (black) charger clamp to an engine or chassis ground.

3. Charge the battery following the battery charger manufacturer's instructions.

 

[Greg2060]

Charger Connected to Engine or Chassis Ground - Preferred Method

NOTICE: Do not connect the negative (black) charger clamp directly to the battery monitoring sensor, it must be connected to an engine or chassis ground to relearn the battery's state of charge.

1. Connect the positive (red) charger clamp to the positive battery post.

2. Connect the negative (black) charger clamp to an engine or chassis ground.

3. Charge the battery following the battery charger manufacturer's instructions.

So the tab off the BMS is not a good point to attach? I thought it was

 

[Ducati1098]

So the tab off the BMS is not a good point to attach? I thought it was

That's fine. Any good ground other than the negative post. It just needs to be on the backside of the BMS sensor

 

[Greg2060]

That's fine. Any good ground other than the negative post. It just needs to be on the backside of the BMS sensor

Thanks!

 

[Brian_B]

So the tab off the BMS is not a good point to attach? I thought it was

That's exactly how I hook mine up.

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