Battery Update

[Larmo63]

I have a predatory battery draw that is hard to figure out on my ‘86 Carrera. No rhyme or reason to it, I thought electric window switches, sunroof switch, even the glovebox light switch.

I still haven’t nailed it down.

It got me thinking I would buy a new smaller battery (Odyssey style) and a Rennline cage for it with a cut-off switch. My idea is to guard the battery from the car drain.

Anybody have battery (make and model #) suggestions for me? The new ones I’ve looked at don’t have near the CCA that the car manufacturer says is needed and this has me questioning.

I had an Odyssey PC925(?) in my Targa, but what is the ”latest” opinion on lightweight batteries?

Thanks in advance and pictures would be clutch!

Happy New Year!

[emac911]

They make battery terminals that are also cutoff switches if you want something simple.

You can take a test light and put it between the negative battery terminal and the negative cable. If you have a drain the light will come on, maybe just barely. Then start pulling fuses to try and isolate the circuit the parasitic drain is coming from. Simple quick test.

[tschall]

I would highly recommend you follow emac911's advice. Spend a little time to get it properly sorted. It really is simple to isolate, then a bit harder to nail down. I had a few drains on my '86, now it sleeps well for 6 weeks or longer with still 12.8V to crank.
My battery is a LifePo4 drop in Group 48 OEM Anti-Gravity lithium battery. Pricey but light !
Happy New Year and good luck!

[Bill Douglas]

I had a drain on the SC.

I checked each fuse wit the multimeter and found the guilty one. A bit weird (fuse for air con or something I didn't even have) so I pulled that fuse out and it's been fine ever since.

[john walker's workshop]

Dome light switches in the A pillar can fail to ground when the door opens and leave the window relay activated. If the window goes up/ down with the key off and door open, that's a draw. It's a carrera thing.

[Larmo63]

My windows do work with the key off and when open.

Hmmmmm?

[Larmo63]

I went to buy a PC925 battery and the Batteries+ store showed me a superseded model they stock.
It’s about half their size of the stock (boat anchor) battery.

Any comments on these?

They don’t have the cold cranking amps Porsche specs 650.

[darrin]

Originally Posted by Larmo63

I went to buy a PC925 battery and the Batteries+ store showed me a superseded model they stock.
It’s about half their size of the stock (boat anchor) battery.

Any comments on these?

They don’t have the cold cranking amps Porsche specs 650.

330a -- https://www.odysseybattery.com/products/ods-agm28l-battery-pc925/ --

Personally, I'd go with a Group 48 AGM -- smaller/lighter than the stock Group 49 battery, but will fit w/o modification (there's a second screw down on the battery tray that will accommodate the shorter group 48) -- doing so will give you a lot more reserve power to deal with unexpected drain issues (i.e. it can easily start your car after powering an accidentally-left-on glove box light overnight, something a smaller battery might not be able to do)

[darrin]

Originally Posted by Larmo63

My windows do work with the key off and when open.

Hmmmmm?

Sounds like you found the source of your drain -- presume that your dome lights don't turn on/off automatically when you open/close your doors. If that's the case, your door pin switch has failed/is dirty and is causing the power window relay to remain energized (and drawing power) whenever your car's turned off.

[G450X]

Originally Posted by darrin

Sounds like you found the source of your drain -- presume that your dome lights don't turn on/off automatically when you open/close your doors. If that's the case, your door pin switch has failed/is dirty and is causing the power window relay to remain energized (and drawing power) whenever your car's turned off.

Thanks! I have had a slow drain and this is probably my problem. I have been keeping the old SC on my battery tender to combat the draw, but I might be able to actually fix it now.

[Larmo63]

I’ll dig into the door switches tomorrow.

Thanks, and will report back.

[Cairo94507]

Hi Lawrence - Hope all is well with you. Happy New Year.
Michael

[Quicksilver]

Originally Posted by john walker's workshop

Dome light switches in the A pillar can fail to ground when the door opens and leave the window relay activated. If the window goes up/ down with the key off and door open, that's a draw. It's a carrera thing.

Trust in John to 'off the cuff' immediately point to the hidden issue.
Always amazing!

[Larmo63]

Originally Posted by Cairo94507

Hi Lawrence - Hope all is well with you. Happy New Year.
Michael

Hey buddy!

[ChrisHoover]

It took me a while to trace the current draw on my car. You need a good wiring diagram. I started by measuring current across the pulled fuse terminals. When I found it and it was milliamps, I used the wiring diagram to eliminate the various branches from the fuse. I found a harness passing through the body with no grommet on the body. The shiner was very small but it was there.

I added a Moroso battery lug disconnect. Alas I am not thrilled with it. Twice it has unscrewed while driving. You really have to crank the sucker down. I will replace with a contactor sometime.