Two batteries under the bonnet - what's the deal?

[Nand0]

Hello all

I'm a new joiner here. Just joined as I am looking to purchase a Subaru Forester. I went to see one today, one of them new fangled 2.0 e-boxer thangs, and when I popped the bonnet, I spotted that there are two lead acid batteries in there.

Curious that I am, I have been looking around to figure out why there are two, and if they are in two independent circuits, or if they are wired in parallel, or what it is. But I cannot find this info.

Does anyone know or have a link to some information I can gobble up?

 

Thanks!

[Seasidesam]

Think the smaller Battery is a starting Battery only. Also been reading that a lot of owners are having issues with Battery drain resulting in not being able to start car after car is not run sometimes as little as 4 days. I am now having second thoughts about purchasing a 21 Forester e boxer i test drove today and need to confirm purchase tomorrow

[Cragonmore]

Hi Nand0, the left hand Battery is the stop/start Battery once you are up and running out on the road. The right hand Battery is the ‘auxiliary’ Battery which starts your engine on cold ignition (start up) and powers your auxiliary electronics (lights, infotainment, heating, etc ) it’s the auxiliary battery that’s giving people trouble if not run on a daily basis and not just short local runs. Many examples of this OEM Panasonic battery discharging between 4-7 days (12.5v down to 11.8v), unfortunately looks like I come into that category! I will be looking for the dealership to upgrade battery  via warranty to give me more ‘time’ before discharged. Other than that eboxer forester is great.

[Nand0]

On 2/13/2022 at 6:52 PM, Cragonmore said:

Hi Nand0, the left hand battery is the stop/start battery once you are up and running out on the road. The right hand battery is the ‘auxiliary’ battery which starts your engine on cold ignition (start up) and powers your auxiliary electronics (lights, infotainment, heating, etc ) it’s the auxiliary battery that’s giving people trouble if not run on a daily basis and not just short local runs. Many examples of this OEM Panasonic battery discharging between 4-7 days (12.5v down to 11.8v), unfortunately looks like I come into that category! I will be looking for the dealership to upgrade battery  via warranty to give me more ‘time’ before discharged. Other than that eboxer forester is great.

Hi Cragonmore

Thanks for your reply. TBH this smells of bad engineering to me. I recently checked out a Toyota Corolla TS, also a hybrid. That ones makes do with a single starter Battery under the bonnet, as you'd expect. I thought Subaru was using the Toyota hybrid system, so found this a bit odd.

I've also noticed the various threads about Battery drain issues, and it has totally put me off.

Subaru, if you are reading, this Battery drain nonsense coupled with your total silence on the matter has just cost you a sale.

[Mr B]

21 hours ago, Nand0 said:

Hi Cragonmore

Thanks for your reply. TBH this smells of bad engineering to me. I recently checked out a Toyota Corolla TS, also a hybrid. That ones makes do with a single starter battery under the bonnet, as you'd expect. I thought Subaru was using the Toyota hybrid system, so found this a bit odd.

I've also noticed the various threads about battery drain issues, and it has totally put me off.

Subaru, if you are reading, this battery drain nonsense coupled with your total silence on the matter has just cost you a sale.

It a case of toyota share some of the tech, Issue is a mess and thought they learnt after the diesel crank fiasco .
Unfortunately most new cars are an expensive misery to live with, you far better keeping your money and hand picking better made older vehicles .
I got no idea why people waste 25K-35K on new garbage so easily, I wouldn't want newer vehicles if given to me free . awful quality and engineering .
Nothing eco about newer cars, most will be scrap in 8 years and filled garage scrap/waste bins with parts/chemical waste and emptied owners bank accounts thanks to endless faults .

[Cragonmore]

Update to my previous post - as expected the Battery ’failed’ when dealership tested it at my request when in for cars 1st Service. New Battery installed under warranty. Will interesting to see how this one holds up. ( replacement was a VARTA Blue Dynamic D47 60 Ah CCA 540)

[Mr B]

20 minutes ago, Cragonmore said:

Update to my previous post - as expected the battery ’failed’ when dealership tested it at my request when in for cars 1st Service. New battery installed under warranty. Will interesting to see how this one holds up. ( replacement was a VARTA Blue Dynamic D47 60 Ah CCA 540)

The Battery life is short thanks to high parasitic draw when vehicle in sleep state and inefficient charge control all of which basically poor engineering choices .
It a massive problem with so called eco vehicles creating lot of waste thanks to part and vehicle short lifespans thanks to the garbage engineering and garbage part quality and wasting owners money by the bucket load .
It not exclusive to Subaru, caveat emptor .
A genuine Battery in a Japanese car use to last close to 8years, today you will be lucky if the whole eco car still cost viable last 8 years and it probably used over 8 batteries as well lol . environmental genius !