‘99 S70 Battery Killer

3iggy · Post by **3iggy** » 05 Mar 2021, 17:24

I have a well loved S70 that’s been in the shop at least three times over the past three winters for murdering its battery. The first time, we assumed that we bought a bad battery. Then the next winter, the second new battery died. The shop has ran diagnostic tests, they’ve kept it for days, and they can’t seem to figure out why my car kills its battery every winter, I can charge it when the temperatures rise and it will keep starting until one day in winter it will die and not reliably start until the weather gets warm again. It’s bizarre and I’m not terribly handy with cars, but I thought I’d put this out there and see if anyone has any thoughts? It’s horribly frustrating.

Post by **RickHaleParker** » 05 Mar 2021, 18:04

Do you do a lot of short trips?
How many miles a year do you put on it?

Post by **abscate** » 05 Mar 2021, 19:19

You need someone who can trace electrical shorts , a skill not in most mechanics toolboxes nowadays. They just want to unbolt stuff and replace

The 1999 model is the first year where stuff begins to go fully electronic, so it’s more sophisticated than the -1998 models.

By any chance, are you having trouble with your courtesy lights not going off? I have a 1999 with a minor problem that I’ve been chasing for a while

Worst case, you can up install a battery switch until you solve it , details to come

3iggy · Post by **3iggy** » 06 Mar 2021, 06:40

Thank you both for replying!

I do make short trips. I bought the car in 2014 with 225k on it and only just hit 250k.

Also, I believe I’ve had some trouble with the interior lights in the past. I turn all the lights off before shutting the car off now. And a battery switch doesn’t sound like a bad idea!

Post by **scot850** » 06 Mar 2021, 09:21

Also check the glovebox and trunk lights don't stay on. Easily tested by using cell phone on video mode to check when they lids are closed.

The glovebox issue for me affects 850's more but still worth a check. Neither is affected by turning interior lights off. Nor are the red door markers at the back of the doors.

The other process is to remove the ground cable from the battery and connect a multimeter between the cable and the battery and see if there is any drain going on. Then pulling fuses to see which circuit it is on. Do not open the doors when doing this as you can fry your multimeter or blow a fuse in it if it has one. Check on current setting. Up to 50mA is not un-common in a normal car.

Neil.

Post by **abscate** » 06 Mar 2021, 12:11

3iggy wrote: 06 Mar 2021, 06:40 Thank you both for replying!

I do make short trips. I bought the car in 2014 with 225k on it and only just hit 250k.

Also, I believe I’ve had some trouble with the interior lights in the past. I turn all the lights off before shutting the car off now. And a battery switch doesn’t sound like a bad idea!

Hide the children before you read this thread. On the 1999 the lights activated by grounding through the immobilized module 2/76. On high mileage cars I suspect the power transistor that does this gets leaky and causes both faults in the lights and current drain of 150-260 mA. That can drain the battery in 3-6 days

viewtopic.php?f=1&t=88623&hilit=1999+S70NA

Post by **RickHaleParker** » 06 Mar 2021, 13:14

3iggy wrote: 06 Mar 2021, 06:40 I do make short trips. I bought the car in 2014 with 225k on it and only just hit 250k.

You do not drive it enough for the alternator to maintain the health of the battery. The battery is constantly deprived of a full charge.

The problem is called Battery Sulfation. The lead plates are converting to Lead Sulfate Crystals. This dismisses the capacity of the battery.

The practical solution for you is to use a battery maintainer. To keep the battery fully charged. The 110V plugin type are $15 - 20. Which is best for the battery . You install this on your car and keep it plugged in when the car is at home. The con is you need to remember to unplug it before you drive off.

The second type is a Solar battery maintainer. These can make a difference and might suit you quite well. A good setup will cost you more then the plugin. I recommend building one with a Solar panel and a PWMCC ( Pluse Wave Modulated Charge Controller ). You can put the solar panel on the rear interior deck. PWMCC in the trunk. Then run wires from the PWM CC to the battery. Park the car at home with the rear window facing south. The pro is you do not need to remember to unplug it before you drive off.

Do not run out and buy another battery. Battery Sulfation is reversible. You need a smart battery charger with a pluse mode as in PMW. The pluse mode will convert the Lead Sulfate Crystals back into Lead. The float charge mode can do it also but not as fast or as reliable. It can take day or week to reverse it but if the battery not way way way gone, it will get there.

A good plugin Battery Maintainer, a modern smart battery charger or a Solar PWMCC will get you to where you need to be.

Post by **abscate** » 07 Mar 2021, 05:03

RickHaleParker wrote: 06 Mar 2021, 13:14
3iggy wrote: 06 Mar 2021, 06:40 I do make short trips. I bought the car in 2014 with 225k on it and only just hit 250k.
You do not drive it enough for the alternator to maintain the health of the battery. The battery is constantly deprived of a full charge.

The problem is called Battery Sulfation. The lead plates are converting to Lead Sulfate Crystals. This dismisses the capacity of the battery.

The practical solution for you is to use a battery maintainer. To keep the battery fully charged. The 110V plugin type are $15 - 20. Which is best for the battery . You install this on your car and keep it plugged in when the car is at home. The con is you need to remember to unplug it before you drive off.

The second type is a Solar battery maintainer. These can make a difference and might suit you quite well. A good setup will cost you more then the plugin. I recommend building one with a Solar panel and a PWMCC ( Pluse Wave Modulated Charge Controller ). You can put the solar panel on the rear interior deck. PWMCC in the trunk. Then run wires from the PWM CC to the battery. Park the car at home with the rear window facing south. The pro is you do not need to remember to unplug it before you drive off.

Do not run out and buy another battery. Battery Sulfation is reversible. You need a smart battery charger with a pluse mode as in PMW. The pluse mode will convert the Lead Sulfate Crystals back into Lead. The float charge mode can do it also but not as fast or as reliable. It can take day or week to reverse it but if the battery not way way way gone, it will get there.

A good plugin Battery Maintainer, a modern smart battery charger or a Solar PWMCC will get you to where you need to be.

Rick, do you have a model you like for a pulse mode charger ? I need to buy a charger for the cottage and will likely use my old Schumacher and buy a PWm for home base

3iggy · Post by **3iggy** » 07 Mar 2021, 05:11

These are all great suggestions! I’m going to look into them. I feel more hopeful about the situation. A person at the shop I take my car to told me the last time I had it towed in to test that I needed to buy a new car, but I don’t want a new one.

I’ll update later.

Post by **abscate** » 07 Mar 2021, 05:37

Sure a new car is nice, but not a new car payment.

Core dump on managing low use batteries

One of our cars gets short runs, so in winter I often top off the battery on weekends to keep it fully charged. In the burbs/ driveway you can use an extension cord. In urban areas you might have to rotate batteries and charge in the apartment. You can rig wires so you can swap batteries without resetting the ECU or radio.

The compact Li battery packs are great for a jump now are about $50. Keeping them inside keeps them warm amd higher performing, as well as topped off on charge