Flat Battery alarm - MG-Rover.org Forums
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post #1 of 9 (permalink) Old 20-11-2016, 11:55 Thread Starter
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Flat Battery alarm

Hi, I've had similar problems before but it seems cold weather brings them on. I only use my 54 ZR about once a week, and during cold periods I have problems with the battery going flat. This is the first time this year that it's happened.

I've got a mobile jump starter battery that I want to use. I can unlock the doors using the key in the door and pop the bonnet but once I connect the charger the alarm goes off. I'm guessing the battery is completely dead. I left it for about 5 minutes charging and it did turn on the electronics inside but it wasn't enough to start the engine. After that the alarm just kept going off, so I gave up so as not to have my neighbours kill me. Is it possible to disconnect the alarm by taking a fuse out so I can do this in silence?
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post #2 of 9 (permalink) Old 20-11-2016, 12:04
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You either need to...

use the car more and charge the battery

Charge the battery from time to time.

or change the battery due to it being on its last legs if the above doesnt work.

Lack of use will reduce the life of a battery.
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post #3 of 9 (permalink) Old 20-11-2016, 23:27
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Originally Posted by bolozenden View Post
........ once I connect the charger the alarm goes off. ?
Always, and I mean always disconnect the battery leads from the battery when charging it from an outside source. If you put the battery on charge from an external charger connected directly to the battery terminals and leave the battery leads attached, you stand a fair chance of doing damage to the engine ECU in particular.

Charge the battery off the car, then re-attach the battery cables. If you have the Lucas alarm system (squarish black remote fob/plip), the alarm will sound on reconnection of the battery and you will need to press the unlock button on the fob several times in quick succession to resync the fob to the system and switch the alarm off.

With the Pektron system which has a black and grey round fob/plip (fitted from July 2003), there is no resync procedure needed, and one press on the unlock button should turn off the alarm.

If your battery has become fully discharged (as it sounds as though yours has done), it will need a prolonged charging to bring it up to a point where the electrical systems and alarm will function correctly. In this case, if the Pektron system alarm goes off without sufficient charge in the battery for the system to operate, the alarm siren will sound continuously from its backup battery until a sufficiently charged battery has been fitted to allow you to disarm the system with the fob/plip. Note that a very low voltage from the car battery over a period can cause damage to the Pektron SCU where one of these is fitted, and this can cause you a whole raft of issues. Best to keep the battery well charged or disconnect it completely if leaving the car unused for a prolonged period.

If you jump start the car, always connect the negative pole of the slave battery or booster to an earth point on the car (the engine block is a sensible place) and only connect the positive pole of the slave to positive pole of the car battery - connecting both poles of the slave/booster to the car battery can also cause damage to the engine ECU and other electrical controllers.
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Last edited by Man in the Car; 20-11-2016 at 23:33.
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post #4 of 9 (permalink) Old 21-11-2016, 02:27 Thread Starter
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Got it jump started, but it did take a long while of being connected up to get it to start. I took it out for a good half hour drive about 6pm to give it a decent boost. Now at 3am I can hear it sitting outside making a fast "ticking" sort of noise?! It's not the full alarm thank god but I can still hear it from inside?
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post #5 of 9 (permalink) Old 21-11-2016, 07:35
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Very valuable informations and very careful & cautious instructions.
Thank you @Man in the Car, I shall be less ignorant from now onwards!
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post #6 of 9 (permalink) Old 21-11-2016, 10:10 Thread Starter
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A slighty less stressed update,but still none the wiser: It was still making the noise this morning so I've disconnected the battery and it's still making the noise?
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post #7 of 9 (permalink) Old 21-11-2016, 12:03
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It does seem like it is time for a new battery which would eliminate one possible cause of your problems. Ebay has several reasonable spec. 063 batteries (suitable for petrol engine 25/ZR) for under 30 including next day delivery.

Last edited by deebee; 21-11-2016 at 12:11.
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post #8 of 9 (permalink) Old 21-11-2016, 15:32
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The ticking noise is the BBUS, a back-up alarm that's triggered when your main engine battery is not producing enough power to maintain the main alarm sounding. Completely charge up your battery or connect a new battery to fix problem.
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post #9 of 9 (permalink) Old 21-11-2016, 17:05
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There is only the one alarm siren which is mounted at the rear right of the engine bay as you stand in front of the car - it has its own back up battery to prevent thieves from silencing the alarm by disconnecting the main car battery. Where the back up battery is 100% charged, it can run the alarm continuously for two or three days!

The clicking noise will be from the alarm still trying to sound (it is probably damaged or waterlogged, or the back up battery has now become discharged and not providing sufficient power to make the siren sound) and will probably need to be replaced.

If the fob button will not operate the central locking with the car battery fully charged, it is likely that that either the fob battery is flat (or not inserted correctly and not engaging the contacts properly), or there is a fault in the SCU - either water ingress has damaged the radio reciever circuit, or the flat car battery has led to damage or memory loss within the SCU. If the fob is not communicating with the SCU to work the central locking, it won't be able to turn off the alarm system either.

If the problem is the SCU, you will need the assistance of a specialist and I would recommend contacting technozen for advice (https://www.technozen-electronics.co.uk/).

You may find the following thread useful to help diagnose possible SCU problems and assist with its removal if necessary: Pektron SCU/BCU.

Am I right in thinking that you had a new car battery back in February? - I would be surprised if it has expired already tbh, so I think the battery running flat in only a week may be due to a parasitic drain - you would need to disconnect the battery negative lead and put a multi meter between the battery negative terminal and the earth lead - you shouldn't have more than about 30 milliamps with all the car electrics switched off. If it is much more than that, you will need to find the culprit by a process of trial and error (disconnect electrical components individually and check for any reduction in the drain). It could be the radio, a stuck or faulty door switch (or bonnet switch) among other things, or even damaged wiring causing a short (check the tailgate loom for damage as well as the engine bay wiring; although such wiring damage usually gives rise to other more readily apparent symptoms).
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