Confusing dead battery
Discussion
I've read a number of old threads on battery drain but just looking for any other comments.
I replaced the battery over winter with an Odyssey one in the footwell for a little extra leg room, so far so good, the car is an SE and garaged with an accumate usually. I went to FoS a couple of weeks ago, about an hours drive each way and parked up the Griff in the garage and left it. I didn't hook up the accumate as it can sit for a few days or so without it and I've done this before without problems.
The next weekend I went to move the Griff and it was dead, put a meter over the battery and it was about 5v!
Disconnected the battery and charged it to high 13v and set about reading threads on parasitic drain. This weekend I started to look at checking for battery drain and when the courtesy relay/timer clicks off I don't seem to have a problem. My meter isn't allowing me to go lower than 100mA so I've ordered one with a lower scale to be sure but as 100mA is the lowest it can show I'm assuming it's rounding up.(it's showing 0.01 on a 20A scale)
The car started fine, the battery shows ~14v on idle and when switched off the battery is now showing just over 13v after being left a couple of days including a start to move it and using the windows a few times.
I've Also checked for AC at the battery (sign of a dodgy alternator) and got 0v. When I get the new meter I'll check for drain again but assuming I get less than 50ma I'm a bit stumped.
I think the PO did have some alternator/battery issues (I've owned it about 2 years now) I believe the alternator was replaced or tested so I'm wondering if it could be bad after getting hot, is that feasible?
If I do hook up the new meter and have less than 50ma drain where do I go next?
Thanks
Mags
I replaced the battery over winter with an Odyssey one in the footwell for a little extra leg room, so far so good, the car is an SE and garaged with an accumate usually. I went to FoS a couple of weeks ago, about an hours drive each way and parked up the Griff in the garage and left it. I didn't hook up the accumate as it can sit for a few days or so without it and I've done this before without problems.
The next weekend I went to move the Griff and it was dead, put a meter over the battery and it was about 5v!
Disconnected the battery and charged it to high 13v and set about reading threads on parasitic drain. This weekend I started to look at checking for battery drain and when the courtesy relay/timer clicks off I don't seem to have a problem. My meter isn't allowing me to go lower than 100mA so I've ordered one with a lower scale to be sure but as 100mA is the lowest it can show I'm assuming it's rounding up.(it's showing 0.01 on a 20A scale)
The car started fine, the battery shows ~14v on idle and when switched off the battery is now showing just over 13v after being left a couple of days including a start to move it and using the windows a few times.
I've Also checked for AC at the battery (sign of a dodgy alternator) and got 0v. When I get the new meter I'll check for drain again but assuming I get less than 50ma I'm a bit stumped.
I think the PO did have some alternator/battery issues (I've owned it about 2 years now) I believe the alternator was replaced or tested so I'm wondering if it could be bad after getting hot, is that feasible?
If I do hook up the new meter and have less than 50ma drain where do I go next?
Thanks
Mags
It is likely what you think it is.
But one thought crossed my mind reading this.
If your 100 amp fuse has cracked or even completely broken, you could have done part of that journey on the battery, not the alternator, and arrived home with a well discharged battery.
The 100 amp fuse is physically located under the car against the chassis rail, next to the sump on the driver's side, in a black fuse holder. You need to unbolt it and take it out of the holder to be sure it is intact. Electrically it is between the alternator and the battery/fuse board.
I speak from experience - when I first had my Chimaera, I drove from Wisbech to Milton Keynes, 66 miles, for a concert at Wavendon.
I don't know at what point my fuse failed, but when I came back to the car after the concert the battery was flat. We bump started it, but after about 5 miles it ground to a halt. RAC were called, and while I waited I described the symptoms on PH on my iphone. By the time the RAC arrived i knew that the issue was 100 amp fuse failure, and where to find it. RAC changed it, jump started the car and all was well.
But one thought crossed my mind reading this.
If your 100 amp fuse has cracked or even completely broken, you could have done part of that journey on the battery, not the alternator, and arrived home with a well discharged battery.
The 100 amp fuse is physically located under the car against the chassis rail, next to the sump on the driver's side, in a black fuse holder. You need to unbolt it and take it out of the holder to be sure it is intact. Electrically it is between the alternator and the battery/fuse board.
I speak from experience - when I first had my Chimaera, I drove from Wisbech to Milton Keynes, 66 miles, for a concert at Wavendon.
I don't know at what point my fuse failed, but when I came back to the car after the concert the battery was flat. We bump started it, but after about 5 miles it ground to a halt. RAC were called, and while I waited I described the symptoms on PH on my iphone. By the time the RAC arrived i knew that the issue was 100 amp fuse failure, and where to find it. RAC changed it, jump started the car and all was well.
QBee said:
It is likely what you think it is.
But one thought crossed my mind reading this.
If your 100 amp fuse has cracked or even completely broken, you could have done part of that journey on the battery, not the alternator, and arrived home with a well discharged battery.
The 100 amp fuse is physically located under the car against the chassis rail, next to the sump on the driver's side, in a black fuse holder. You need to unbolt it and take it out of the holder to be sure it is intact. Electrically it is between the alternator and the battery/fuse board.
I speak from experience - when I first had my Chimaera, I drove from Wisbech to Milton Keynes, 66 miles, for a concert at Wavendon.
I don't know at what point my fuse failed, but when I came back to the car after the concert the battery was flat. We bump started it, but after about 5 miles it ground to a halt. RAC were called, and while I waited I described the symptoms on PH on my iphone. By the time the RAC arrived i knew that the issue was 100 amp fuse failure, and where to find it. RAC changed it, jump started the car and all was well.
Thanks, wouldn't this impact seeing 14v at the battery or could a cracked fuse mean the charge could be intermittent or fine when cold/stationary and break when hot/moving?But one thought crossed my mind reading this.
If your 100 amp fuse has cracked or even completely broken, you could have done part of that journey on the battery, not the alternator, and arrived home with a well discharged battery.
The 100 amp fuse is physically located under the car against the chassis rail, next to the sump on the driver's side, in a black fuse holder. You need to unbolt it and take it out of the holder to be sure it is intact. Electrically it is between the alternator and the battery/fuse board.
I speak from experience - when I first had my Chimaera, I drove from Wisbech to Milton Keynes, 66 miles, for a concert at Wavendon.
I don't know at what point my fuse failed, but when I came back to the car after the concert the battery was flat. We bump started it, but after about 5 miles it ground to a halt. RAC were called, and while I waited I described the symptoms on PH on my iphone. By the time the RAC arrived i knew that the issue was 100 amp fuse failure, and where to find it. RAC changed it, jump started the car and all was well.
I know the simplest answer is usualy the right one!
Possible sources of current drain include the courtesy light relay that you have mentioned, the alarm/immobiliser and to a much less extent the alternator itself ( only a few milli amps) I completely isolate the battery when the car is garaged this includes 6 months over winter. I have a conventional battery installed in 2008 by the RAC( no idea what the make is) following failure of the original. It is still fine and is never connected to an accumate, I give it an occasional charge during the winter.
Loubaruch said:
Possible sources of current drain include the courtesy light relay that you have mentioned, the alarm/immobiliser and to a much less extent the alternator itself ( only a few milli amps) I completely isolate the battery when the car is garaged this includes 6 months over winter. I have a conventional battery installed in 2008 by the RAC( no idea what the make is) following failure of the original. It is still fine and is never connected to an accumate, I give it an occasional charge during the winter.
Thanks, I'm checking with the doors closed and courtesy lights off/timer passed. I think my old Cerb used to need the boost after a few weeks so it's a habit to use a battery optimiser now.I’m having this same problem right now. Had the alternator tested and it was fine. Battery was replaced with a higher 800 amp unit. And it worked for a week before draining the new battery.
All of this started on the trip to Woodwork in Michigan USA. Drove for 2 hours and the dash gauge was reading 13v. We had fun for the weekend and on the way back 2 hrs I realized my gauge was now at 11v. and it has remained there with the new battery.
Do you think that 100a fuse might be my issue? I’m traveling so I don’t have a lift. And it sounds like I would need one.
All of this started on the trip to Woodwork in Michigan USA. Drove for 2 hours and the dash gauge was reading 13v. We had fun for the weekend and on the way back 2 hrs I realized my gauge was now at 11v. and it has remained there with the new battery.
Do you think that 100a fuse might be my issue? I’m traveling so I don’t have a lift. And it sounds like I would need one.
Trickle charging (Accumate, Optimate or whatever) IME can disguise a knackered battery.
I had a Cerbera in 2019 that the previous owner always kept on trickle charge. It would go flat within just 2 days parked at home.
Had to replace the battery for a new one. It wouldn't hold full charge (ie 12.6V) for more than a few hours.
I had a Cerbera in 2019 that the previous owner always kept on trickle charge. It would go flat within just 2 days parked at home.
Had to replace the battery for a new one. It wouldn't hold full charge (ie 12.6V) for more than a few hours.Problem resolved. Big thanks to all the guys recommending the 100a fuse as the first check point. That's exactly what it was. It had arced but was still conducting enough to start the car but also sucking off about 3v while the car was running. It's all replaced and cleaned up and now both the car and I are very happy!
The car would start with a broken 100A fuse down on the chassis with a good battery, but the battery would drain fast! Glad you found it. 
It competes the circuit for the alternator to charge the battery and if it had been completely bust, your low battery light would be on. I had one cracked on a previous TVR and the battery charging light had a dull glow to it which suggested to me what it was.
It competes the circuit for the alternator to charge the battery and if it had been completely bust, your low battery light would be on. I had one cracked on a previous TVR and the battery charging light had a dull glow to it which suggested to me what it was.
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