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Start/Stop travails

Some of the regulars here will recall my issues with the stop/start feature on my Jeep (where the engine will shut off at stop signs/lights and restart when the brake is released). Well, I have it all figured out now.

Per the advice of several posters here and after a discussion with one of my neighbors I purchased a battery tender/manager. This will recharge the battery and when the charge is full will add a charge only when the battery starts to lose it’s charge. I hooked it up and low and behold (or high and discard, as you will) it worked.

So here is the story: I hooked it up at about 2:30 yesterday afternoon and it indicator light showed it was charging. I checked again throughout the day and it was still charging when I went to bed. I checked when I got up this morning a little before 6:00 and it was still charging. I reread the instructions and noted you are supposed to shut off everything that pulls juice from the battery. I park in a closed and fairly secure garage but my habit is to set the alarm when I’m done with my car for the day. So I shut off the alarm. It still showed it was charging. I walked from the garage to the den and then back again and it showed the battery was charged. Disconnected the manager and drove the car this morning and the stop/start is back. So here’s the takeaway: the alarm draws enough juice that the manager was barely making headway - so I will no longer set the alarm when the car is in the garage. In addition, during talks with the dealer they indicated the communication portal (UConnect for FCA, Sync for Ford, OnStar for GM) will talk to your car, even when it’s off, which will further draw some juice from the battery.

Interesting story and glad it worked for you.

Good for you for solving your Jeep’s start/stop frustration. However, if you drive your Jeep most every day recharging the battery with a tender shouldn’t be necessary. I expect you may have a problematic starter motor or something. A few winter’s back my Corolla was acting up on cold (for San Jose) morning first starts of the day; cranking wasn’t very robust, and occasionally I’d get some clicking. I solved that symptom 100% by charging the battery with an ordinary battery charger on the 2 amp rate for an hour or two each day. Back to robust cranking even on cold mornings. But eventually I needed a new battery and I decided to install a new starter motor at the same time as the new battery, and after that the battery charger was no longer needed.

I generally drive it somewhat about 5 days a week; there’s usually 2 days I don’t drive it at all. Actually, I think the alarm is draining the battery - not enough so that it won’t start, but enough to disable the start/stop feature. That’s why I think it took so long to recharge my battery - the charger could barely stay ahead of the drain of the alarm. My neighbor is also retired and he’s had this issue with his last 2 trucks. His old truck ('90s F350) was seldom driven due to the poor mileage (he bought it to tow his 35 foot trailer, which is now sitting because is wife is no longer up to long trips). His new truck (2018 F150 King Ranch) had the same issue with his start/stop and was told the same thing by his dealer - to use a battery manager to keep his battery charged.

Irregardless of what the dealer said, there is still a problem here. Assuming this is a 2 amp charger, that means the alarm system draws almost 2 amps. That will discharge a typical new battery in about 40 hours or less than 2 days. That, if true, would result in every new car having a dead battery soon after purchase, not a tolerable situation, either by the dealer or the drivers.

(if your charger has a different rating, you can adjust the above numbers)

Have you ever measured how much current the alarm uses? Easy enough to do. Here’s how I do it. I turn the engine and everything I can to “off”, key removed from ignition and in my pocket. Next remove the negative ground cable from the battery and insert an amp-meter in series to reconnect the battery ground. Start with the amp meter on its highest range, 10 amp usually. I wouldn’t expect an alarm system in its normal monitoring state to use more than 200-300 mA (0.2 to 0.3 amp), if even that. This method measures both the alarm system and the rest of the car. The rest of the car’s electronics in the off-state shouldn’t be using more than 50-100 mA. It may take a half-hour or so after reconnecting the battery ground (via the amp meter) before all the computers turn off however.

There’s a downside to this test to be aware of. Disconnecting the battery can sometimes cause problems upon reconnecting. The engine may not start or idle properly and has to go through an idle learning process first; and disconnecting the battery can cause the computer’s readiness monitors to enter a not-ready state, preventing emissions testing.

I think the problem is trying to setting the alarm with the hood open, the BCM is waiting for all the doors, hood and lift gate to close before going into sleep mode. This is something you need to be aware of before beginning an ignition off draw test which I would advise against.