987 Battery Disconnect For Storage - What goes wrong? Are there fixes?

Hello from Engand, I'm Thomas, and I'm new to the forum. I already own a Macan , but am considering a 'cheaper' Boxster / Cayman 987 to store in another part of the country. I've found a covered and secure parking space, in fact several, but unfortunately non come with power. I need a car to get around when in this part of the country, and would prefer to make it a fun one However, it's likely that the car could go unused for 3-4 weeks at a time, and I've been researching what to do about the battery , given that I have no power / battery charging / tending facility. I had a quick search on this topic, in various forums, and found various bits of information in various places. I'm trying to piece together a picture, before I commit to buying the car. I have already ruled out a BMW M4 for this reason because the battery is inaccessible and because it's a Lithium type, it costs ~$1200 to replace, when it eventually dies from this kind of usage cycle! Previously I had a B5 Audi RS4, and I added one of those twist knob battery isolators to one of the battery terminals. I would pop the bonnet, lock the car and then isolate the battery , which would still self-discharge, but far slower than with anything attached. I'd leave the bonnet popped and put a car cover on. This worked perfectly for many years, other than the radio code / dashboard time needing resetting when I came to use the car. My research suggests that this might not be the case with the 987 family. So here are my considerations, and I'd welcome feedback / thoughts from everyone. If I go ahead, I'll reply with a full write-up for how I did it. - I could replace the battery with an AGM type that would withstand deeper discharge, and therefore better withstand this kind of intermittent usage / load. - I think I could pop the bonnet / frunk, lock the car, isolate the battery , leave the bonnet on latch and cover the car. This also makes it a lot harder to steal of course! An alternative would be to install a wireless battery isolator, removing the need to fiddle with the bonnet. - After some weeks, probably minutes actually, everything in the car will be fully discharged. Now the problem with BMW 's (I've ready) is that they can go into 'transport mode', which can only be undone by the dealer, so this is a no go. Too much effort. - Upon reapplying the power, I would expect the car to 'boot up' as per normal, as if the battery has been removed for swap. However, any smaller batteries / capacitors as part of the car electronics will have depleted in the time that the car is left, so unless all the car settings are written to flash memory, they'll be lost. - However, it seems that some people don't have this problem - everything is fine. Others do have this problem, and in particular there are reports that the heated seats seem to stop working. The solution it seems is that the car has to go to the dealer or DIY recoded with the Durametrics system. This seems to be a bit of a faff to be honest, and it would seem that it's the result of a firmware fault in one of the Porsche computers. It feels unlikely that they didn't fix this in a later firmware upgrade, and therefore it might not affect cars made after a certain date. Or it might be due to something else. - Another option is that install a 2nd battery into the frunk and add some 2nd battery isolator / conditioning circuit so that the 2nd battery supports the first, but doesn't overload the alternator . However, it feels like I wouldn't be doing enough driving to ensure that both batteries would be fully charged which would probably require some long road-trips. I think that disconnecting the the battery is the elegant option with an expectation that the AGM battery would need to be replaced every 18 months and that's just part of the cost. However, it becomes a pain to have to recode it every time I come to use the car, and England is cold, so I'd really like those heated seats to work! A few questions of you if I may please... - Does anyone know if there are other potential faults that I should be aware of? - Does anyone know if there is a permanent fix to the heated seats failing? - Does anyone know if these issues are related to a particular set of build years - i.e. was it a problem that was fixed later on in the car's manufacturing life? I can't believe that I'm the only one with this problem, but there don't seem to be many people documenting solutions other than charge the battery / replace it / visit the dealer! Many thanks in advance for the support! Cheers, Tom.

Any sunshine nearby? A smallish solar panel could keep the battery charged - just run a thin wire from the car to the roof.

Good idea, but sadly not. It's in an underground carpark.

Based on my experience, if the battery is in good shape (e.g. fairly new) it should be fine going 3 or 4 weeks. In winter I've often left my 987 for that long between uses or without connecting the battery maintainer. Any longer periods than that might become an issue but if you can get to it that often, and if the car is in a covered garage that doesn't get really cold, the parasitic draw won't be enough to significantly discharge the battery .

How about using a battery jump pack? Keep it at home, charge it before heading out to pick up the Cayman . https://www.amazon.com/gp/product/B000JFJLP6/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

If 3 to 4 weeks is you time line for non use then this should not be a problem. Make sure that your car is well changed when you park it and locked. The idea of having a jump pack as a back up is a good one!

AGM charges at 14.7, the 987 battery at 14.3. Not sure the 987 will properly charge an AGM battery. You might want to check into that.

You may want to consider a Li-ion battery , they can sit disconnected for much longer periods of time without discharging. The Antigravity RS-30 has an on/off button so you wouldn't have to disconnect anything; just turn it off and it'll be ready for you when you return. Only downside is the bonnet is electrically operated so you'll need a temporary power source, like a Micro Start, to connect to open the bonnet and turn the battery on.

I used an Odessey AGM in my 2007 Cayman for many years with no issues. I kept the car on a trickle charger. I also installed a battery disconnect switch with no issues upon reconnecting.

I live in Bristol..Leaving the car will do it no good. I leave mine for long periods and it's nothing but trouble in the cold damp atmosphere...that is England..keep it warm. I am forever relating corroded pipes, coils, and other parts

Hello, I had the same problem with extended storage and have no means to connect a battery charger at my parking spot. I purchased another battery to connect the with the main battery (Banner), in parallel. The battery I purchased (Exide) is the same type and capacity as the main battery ( AGM , 80 Ah). In the last 2 years, I did not run the car during a 11 week period, while away on holidays, and when I returned the engine started without a problem, both times, after disconnecting the Excide battery . The last step before leaving on holidays, was to switch off the interior surveillance inclination sensor by pressing the key fob locking button twice within 2 seconds, in order to draw the minimum amount of power. I also have a battery charger in my apartment to fully charge both batteries, but one at a time. The only difficulty is lugging the batteries from my apartment to the parking spot. I think this is better than resetting all the electronics. I do not run the engine when both batteries are connected in parallel. When connecting and disconnecting the batteries you always have to make sure that at least one battery is always connected. You have to carefully think through the steps when connecting and disconnecting the battery cables. I also attached a file telling what to do when battery power is lost. Cheers

That’s A pretty good solution but I was this thread on another board. It seems they’ve come up with something along the same lines that you’ve come up with. Create a wiring harness that fits under the hood and is easily accessible and if your battery should go dead simply plug in a “ micro jumper battery “ and hopefully you’ll be on the road pretty painlessly. Posts #33 and # 38 are where most of the info is. https://********.com/forums/987-981-forum/1110823-dead-battery-help-up-creek-3.html

The micro starts work really well, however you're going to ruin your lead acid/ AGM battery in a hurry. They just aren't intended for that depth of discharge and the battery is going to have a short life. This is where a litium ion really helps, not to mention 30-40lbs of weight savings..

If I were to use the “ micro start “ solution to just open the frunk in an emergency situation would you see that as a problem. Also, could you explain how’d I’d be ruining an AGM as I’m not that technical. Thanks

Hello again! Thank you for the additional ideas - I've been lurking and thinking more about this over Christmas. I quite like the dual battery idea, but I need the frunk space to store sports kit that I use when I'm in the locale of the car. I agree that lead-acid batteries do self-discharge when disconnected, but obviously a lot less than if there's even a small parasitic draw from the Microcontrollers in the car. Also I'm thinking that it's cheaper to replace the lead acid battery once every 2 years than buy a Li-ion battery! I'll guess I'll have to see how being only charged from the car once a month works out... I've been trialling with just the battery and I've noticed that it does indeed last about 3-4 weeks. But, I think there could be bouts of longer disuse, so I'm going to trial a slightly different solution. Also I don't want to leave the frunk semi-open for security reasons. So, I'm going to aim to disconnect the battery, except for a small wire through the hidden push switch which can then directly operate the emergency frunk actuator. If I put a diode inline with the signal from the emergency controller, then there should be nothing back-driving that circuit (which will be completely off due to the main battery being isolated). This does have a non conventional requirement to put the battery screw isolator on the positive side of the battery, so that I can still operate the emergency frunk actuator through the push switch... However it seems that this should be an issue ( https://electronics.stackexchange.c...om/questions/230609/why-to-disconnect-the-negative-ground-terminal-not-positive ) since the advice to remove the negative terminal first relates to the safety around a direct battery short. Once I've done the work, I'll write up here how it all went with some photos! Cheers, Tom.

Hello again! Thank you for the additional ideas - I've been lurking and thinking more about this over Christmas. I quite like the dual battery idea, but I need the frunk space to store sports kit that I use when I'm in the locale of the car. I agree that lead-acid batteries do self-discharge when disconnected, but obviously a lot less than if there's even a small parasitic draw from the Microcontrollers in the car. Also I'm thinking that it's cheaper to replace the lead acid battery once every 2 years than buy a Li-ion battery! I'll guess I'll have to see how being only charged from the car once a month works out... I've been trialling with just the battery and I've noticed that it does indeed last about 3-4 weeks. But, I think there could be bouts of longer disuse, so I'm going to trial a slightly different solution. Also I don't want to leave the frunk semi-open for security reasons. So, I'm going to aim to disconnect the battery, except for a small wire through the hidden push switch which can then directly operate the emergency frunk actuator. If I put a diode inline with the signal from the emergency controller, then there should be nothing back-driving that circuit (which will be completely off due to the main battery being isolated). This does have a non conventional requirement to put the battery screw isolator on the positive side of the battery, so that I can still operate the emergency frunk actuator through the push switch... However it seems that this should be an issue ( https://electronics.stackexchange.c...om/questions/230609/why-to-disconnect-the-negative-ground-terminal-not-positive ) since the advice to remove the negative terminal first relates to the safety around a direct battery short. Once I've done the work, I'll write up here how it all went with some photos! Cheers, Tom.