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Left car parked at a hotel a week at Christmas. When arriving back to hotel on Christmas night, the battery was dead. Waited a couple hours for repairman to come and start car. (Never will be without jumper cables again) Finally got car started to discover we must have bumped side door light, as it came on after jumped. Figure this was our fault, as it was there for a week. A few weeks later we drove to FL and spent the night in another hotel. Coming out in the morning, the car barely started. I checked to make sure I had not left anything on. Nothing was on. Car is normally parked in garage and didn't have any more problems. A month later, I was searching for papers in the glove box around 6 in the evening. Forgot to close lid. Next morning around 7:30, I ran out to leave, and the battery was dead. Just doesn't seem right that the battery should be dead from a light in the glove box being on for 13 1/2 hours. Thoughts?
 

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Left car parked at a hotel a week at Christmas. When arriving back to hotel on Christmas night, the battery was dead. Waited a couple hours for repairman to come and start car. (Never will be without jumper cables again) Finally got car started to discover we must have bumped side door light, as it came on after jumped. Figure this was our fault, as it was there for a week. A few weeks later we drove to FL and spent the night in another hotel. Coming out in the morning, the car barely started. I checked to make sure I had not left anything on. Nothing was on. Car is normally parked in garage and didn't have any more problems. A month later, I was searching for papers in the glove box around 6 in the evening. Forgot to close lid. Next morning around 7:30, I ran out to leave, and the battery was dead. Just doesn't seem right that the battery should be dead from a light in the glove box being on for 13 1/2 hours. Thoughts?
What is a "side door light?"
 

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I'm guessing that the week with a light on drained your battery to the point of damage. The jump start and drive brought it back to charge, but the effective Cold Cranking Amps may have been impacted permanently. Then normal starts succeeded, but with little headroom. Then for whatever reason the night at the hotel was stressful, and showed as a struggle to turn over the next morning. Then the glove box pushed an already damaged battery over the edge. IMO.

You can have the dealership test the battery capacity / effective CCA. Running down car batteries (as opposed to something like marine batteries) is really bad for them.

F.S.
 

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The OEM battery is pretty bad to behind with. Im looking to purchase a replacement as soon as I figure out what I can upsize in there from Costco. I usually get 4-5 years out of them.

I believe its a Group 31 currently in there.

I've noticed it dropping under 12 volts after a few days of sitting which is 40%-50% full. Its just waiting to strand me somewhere.
 

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I believe the Ascent has an unusually large parasitic current drain. It's normal these days for cars with sophisticated electronics to have parasitic drains, but my Ascent's battery voltage routinely drops to 11.5 volts after several days of non-use. I've had to charge it several times over the last few months. I'm now keeping a close watch on it. This weekend, if I get a chance, I'll measure the current drain when the car is turned off. This is fairly easy to do with a good multimeter.

Once I measure the parasitic drain, I can then easily calculate the rate of battery discharge if the battery's amp-hour rating is available. I will post the findings here.
 

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I believe the Ascent has an unusually large parasitic current drain. It's normal these days for cars with sophisticated electronics to have parasitic drains, but my Ascent's battery voltage routinely drops to 11.5 volts after several days of non-use. I've had to charge it several times over the last few months. I'm now keeping a close watch on it. This weekend, if I get a chance, I'll measure the current drain when the car is turned off. This is fairly easy to do with a good multimeter.

Once I measure the parasitic drain, I can then easily calculate the rate of battery discharge if the battery's amp-hour rating is available. I will post the findings here.
Nice, I’m going to attach my trickle charger (Optimate 4) on it, while I’d prefer not to, it definitely helps my batteries last a longer.

Just need to figure out where to put the quick disconnect where if I forget it, it will detach as I back up.
 

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I looked at Costco and Autozone for a replacement battery but didn’t see any. Does anybody know which battery would work if we wanted to upgrade? I may just drop some money and buy a better battery.
 

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I looked at Costco and Autozone for a replacement battery but didn’t see any. Does anybody know which battery would work if we wanted to upgrade? I may just drop some money and buy a better battery.
If the issue is a high parasitic current loss, which is what I believe to be the problem, then a different battery won't help much, if at all, unless it has a significantly higher amp-hour rating than the OEM battery. In most cases with lead-acid batteries, physics dictates that to get a significantly higher amp-hour rating, a physically larger battery is required. This may not be possible fitment wise. And don't be thinking that an expensive Lithium-iron battery is the answer, they're even worse with parasitic loss than lead-acid batteries. However, there may be an ultra-premium lead-acid battery out there with a better amp-hour rating than the OEM. We won't know until we do the research. But simply buying a different battery with the same or similar amp-hour rating is most likely not going to help.

Unless the OEM battery has an unusually high self-discharge rate or is defective, which is doubtful since none are older than a few months, then it's all about the amp-hour rating. So unless the OEM battery has a poor amp-hour rating for its size, again doubtful, a new battery won't help much. Given the same amp-hour rating with the same current draw, virtually any battery will discharge at the same rate.

If you wait until I measure the Ascent's parasitic loss, then I'll also supply a simple discharge rate calculation for how long any battery will last without a recharge based upon its amp-hour rating. Then you can decide if a replacement battery will be worth it.

I plan to measure the Ascent's parasitic current loss this weekend if my business doesn't call me away. But if anyone else who knows how to do this can do it earlier, then that would be great. In fact, the more Ascent owners who can do this the better, because then we'll know for sure the real parasitic current draw based upon more than one Ascent.

See below on how to do it. However, I would add that it's important not to break the battery connection because this may cause the ECM to go into a mode which may draw more current while it resets. You can keep the power alive while you disconnect the primary battery terminals by using a backup battery, then remove the backup battery after the meter is in the circuit.

https://www.youtube.com/watch?v=KF1gijj03_0
 

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I was able to measure the parasitic current drain on my Ascent and I'm happy to report that there does not appear to be a problem. This is good news because if there was a problem here, it would be next to impossible to fix. The Ascent draws only between 15-25ma when powered down, (i.e. no accy, no ignition, doors closed, all lights off). This is well under the 50ma acceptable limit. 15-25ma is not an unreasonable parasitic load on a battery and should not draw down the charge for any reasonable length of time. I could not find the amp-hour rating of the battery so I could not calculate specifically how long it would last with this load, but a battery of the size used in the Ascent is typically around 37 amp-hours. With a parasitic current loss of only 15-25ma, such a battery should last for many weeks before being fully discharged.

That said, the Ascent can still be tough on a battery. As soon as you open the door, the amperage draw goes up to around 4 amps. And since the lights are delayed before they go off after the door is closed, this adds to the drain. Also, when you turn off the ignition, the headlights stay on for a while as well. All of this can add up. I assume the alternator can keep up with the high powered HK amp, the heated seats, the heated mirrors, the rear window defrost, etc., but the battery may not get the best charge when all these high powered accessories are being used.

I used a 500A battery load tester to test the OEM Subaru battery and the results were not great. The battery is rated for 530 CCA, so to test it a 250A load was applied for 15 seconds (the battery was fully charged just before the test). This was repeated three times within 5 minutes. It passed, but just barely. The tester was right on the line between "OK" and "Replace". This is not impressive for a new battery. The battery is manufactured by Johnson Controls. They usually make decent batteries, but Subaru may have specified a cheaper design to save money, who knows.

Considering all of this, I would probably recommend purchasing a better battery if you have issues with the OEM battery going dead or discharging repeatedly. The question is, are better batteries currently available in the size required? I'll dig into that next.
 

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"The question is, are better batteries currently available in the size required? I'll dig into that next."

This is great stuff, many thanks for your yeoman work!
 

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I have come to be a fan of Noco products. I too dealt with early battery drain issues and sometimes had rough starts. I bought a 4bank charger and currently hook up my ATVs to it to keep the batteries up to charge. Once every couple months, or before a long trip, I will connect the Ascent to condition the battery and get it back up to charge. It will occasionally read around 50-75% when connected. I have not had any starting issues since. I leave the quick disconnect under the hood but leave the hood slightly propped so I never forget to disconnect. I also keep a Noco genius in the trunk to jump on the go without the need of anyone’s help. It has proven to be a great investment for helping others but I have yet to need it myself. I realize people don’t want to spend money on an item to keep you battery charged, but I look at it more as a maintenance item. I used an optima battery conditioner previously on my other Subaru’s. I’ve always had a slightly higher draw due to my dash cam setups.
 

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planning on 500 mile trip then parked for two weeks.
will do trip 1 week after picking up new ascent.
concerning battery would you: not worry about it, replace battery before i go, bring booster cables or disconnected positive terminal?
 

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planning on 500 mile trip then parked for two weeks.
will do trip 1 week after picking up new ascent.
concerning battery would you: not worry about it, replace battery before i go, bring booster cables or disconnected positive terminal?

I had a bad battery but didn't really have issues without a secondary cause. 1. Camping with the hatch open. 2. Listening to the radio on ACC. Or others leaving a light on. Just not turning on the car for two weeks may not be that big a deal. You can always buy a simple battery tester you plug into the car outlet to see the current capacity.
 

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planning on 500 mile trip then parked for two weeks.
will do trip 1 week after picking up new ascent.
concerning battery would you: not worry about it, replace battery before i go, bring booster cables or disconnected positive terminal?
I agree with the posts above. The OEM battery will work fine provided you do not put any unusual load on it when the engine is not running, such as using the sound system, keeping the rear gate open, using the interior lights excessively, etc.

Since the parasitic drain is acceptable, the problem with the battery discharging is most likely due to using light and accessories with the engine off. If you're careful about this then you should be ok.

That said, the OEM battery is a poor choice for this car because it's not a great battery and the car has so many power-hungry accessories. I plan to replace mine with a better battery. I'm doing research on finding a suitable one now.

Carrying quality jumper cables and/or a quality battery pack jump starter is always a good idea. You should have at least one of the two as required equipment.
 

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Just a FYI, the replacement group 35 battery at Costco is $75. I believe it’s 660 CCA vs the stock 550.

Was gonna get one so I’m not stranded somewhere, but thought it was pretty ridiculous I’m getting a new battery for a 6 month old vehicle. I’ll see if they’ll give me a new one when I bring it in for service after showing them my data (2-3 days it’s under 12v)
 

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Just wondering. I’m not up to speed on batteries but there are several types of batteries out there- lead acid, deep cycle, AGM, lithium, etc. if one is upgrading and one wants a bigger power reserve to run an aftermarket sound system and other accessories, what’s the best choice?
 

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Just a FYI, the replacement group 35 battery at Costco is $75. I believe it’s 660 CCA vs the stock 550.

Was gonna get one so I’m not stranded somewhere, but thought it was pretty ridiculous I’m getting a new battery for a 6 month old vehicle. I’ll see if they’ll give me a new one when I bring it in for service after showing them my data (2-3 days it’s under 12v)
I don't think getting another OEM battery will help. The issue isn't with any individual OEM battery, the issue appears to be with the quality of all the OEM batteries. I think Subaru went with a low-cost battery here.
 

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Just wondering. I’m not up to speed on batteries but there are several types of batteries out there- lead acid, deep cycle, AGM, lithium, etc. if one is upgrading and one wants a bigger power reserve to run an aftermarket sound system and other accessories, what’s the best choice?
I researching this right now. I should have something to report very soon.
 
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