Alarm and Frunk Issues - Possibly Battery/Charging Issue

Hi All, An interesting thing happened with my '99 C4 today and I wondered if any of you can help. I used the car last Sunday 18th, a fairly short drive, stop and then back again. Today the central locking didn't work and then the frunk wouldn't open. The car was slightly reluctant to turn over but did so. After the car had been running for a minute or two the frunk opened. I then took it for a 12 mile drive which resulted in the central locking and frunk working at our destination. The battery is a recent Varta from 2024. With limited use should I use a trickle charger? There seem to be no charging issues and the voltage seems fine or can there be other issues with the battery being drained? It is totally standard and has the Porsche CDR-22 Radio so nothing added that could be draining power. Your thoughts appreciated!

Once the battery drops below a certain level, then the alarm ECU goes in to sleep mode. The car can only be opened by the key then. In perfect conditions, i.e. fully charged battery in mild or warm environment and no parasitic drain on the battery should be about 2 weeks. But during cold periods and if the battery is not fully charged and you have maybe a light parasitic drain, then it'll go in to sleep mode after just a few days. Sleep mode is perfectly normal, but it doing it so quickly is not. If you're not going to use it much over winter, I'd either trickle charge it or put up with it going in to sleep mode. With sleep mode, once some juice is put back in the battery, it'll be normal again.

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Thank you Alex. I guess it will take a skilled an car electrician to sort it. I also have a problem with drivers door latch with the window not dropping, could this possibly exacerbate this problem. I do use the car fairly regularly although it hasn't had a decent run over 15 miles for over a month which won't help.

Window drop won't be causing the problem - that's just one of the microswitches in the door. Easy to find out if you've got a parasitic drain. Just need a multimeter to measure power being drawn and start pulling fuses. deMort has posted loads of advice on what to do, use the search and search for parasitic and his username. Here's an example: D Post in thread '986 Battery Drain' 22 Apr 2022 Sorry .. i missed this post last night .. First off .. an amp hound is the best way to locate a parasitic drain these days .. whilst its not used often it is a god send as you can read off the current draw of each individual fuse . Ok .. so i know the 996 does a lambda sensor burn off for approx 30 mins .. this will give the best part of 1 amp discharge on a meter .. to stop it ( cheat ) you pull the dme fuse then reinsert .. I'm not 100 % sure the Boxster does this but it is logical to assume it does . normal test with an amp meter and you leave the car for at least 40 mins .. at... deMort

Thank you Alex and deMort. I will have a look at the fuses when the weather cheers up and do the door latch. I have the part and have researched how to do it and have all the right tools. The interior switch works fine but the exterior is broken. It started happening not long after I got the car.

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Sometimes it's just moisture in the switch on the external door handle. I good blast with the hairdryer sorts it out.

I will give that a go Alex!

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Yes If you can't get a trickle charger with 240v to the car there are also options so let me know But ideally yes the battery needs charging not necessarily all the time but a short journey won't give it enough time to charge. A reasonably flat battery needs over night to charge fully using a trickle charger. Your battery has probably been operating at a medium charge for a while and eventually dipped too low. I used to keep on top of charging all my batteries once a month when I had 6 vehicles but it gets boring quickly.