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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 **** 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 read) 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!
You may be overthinking this. Just disconnect the battery and leave the "bonnet" (i.e. hood) ajar. When you goto drive it, reattach the cables and it should be fine after only 4-weeks. If not, use a portable jumper unit to charge the battery and start the car. The battery on my 09S lasts longer than that even still connected.
This is $50US, which is <39-pounds before all your added taxes.
Hi Thomas,
I have a 987 Cayman (in the UK) and the manual has a page dedicated to what needs doing after a period with the battery disconnected. The two main areas are the PSM and windows which take a couple of minutes total to reset. In the 2011 Cayman manual this is on page 171 under the heading "Putting vehicle into operation".
10-31-2018, 08:39 AM
987 Battery Disconnect For Storage - What goes wrong? Are there fixes?
