Battery going flat

[t0m]

Honda Jazz Mk1 battery going flat if left to sit for a couple of days. At first I thought the battery might be faulty and as it was less than three years old I had it replaced under warranty. Unfortunately this didn't solve the problem and the battery went flat again when the car was unused for a few days.

I hooked up a multimeter for a parasitic drain test and found that the current is reading 110-120mA with everything off which seems high. I checked cabin and boot lights and all are switching off when the doors/boot shut. I then pulled all the fuses one by one but the only one which caused the current to drop to 0 was the one labelled "Back up." I suspect there should be some current draw rather than none so I think that is a red herring.

I've read that a faulty alternator can cause parasitic drain. It reads 14.45V with the engine running so it does work. Unfortunately I couldn't disengage the wiring harness to prove it as there just isn't enough room to get at it. Do you think it is worth having the alternator replaced? Or is there anything else I can try?

[embee]

Quiescent current should be single figures milli-amps.
I've seen relay actuator coils draw 100+mA, check every light switch (fog etc) is in the off position.
I've also see USB adapters plugged into an aux socket draw 120mA with nothing actually plugged into them.

The other thing which caused someone grief was one of the insurance black-boxes plugged into the OBD socket. The first one was taking around 50-60mA, the replacement sent by the insurance company was around 10mA, which is tolerable.

Since you are able to measure the draw with your equipment, I'd continue with disconnecting things. Is "back-up" actually reversing light? If so is there a relay on it?

[sparky Paul]

Is "back-up" actually reversing light? If so is there a relay on it?

No relays, just an old fashioned switch in the gearbox. Fuse for this is in the under dash fusebox, F5 or F1, depending on early/late fusebox.

F8 (under bonnet fusebox) is described as 'back-up' in the Jazz handbook, it's a permanent live that feeds the radio, ECU, instruments, immobiliser, etc., etc..

Here's a bit of a tale though...

Just to confuse matters, if you have a Mr Haynes book, they appear to have mis-transcribed 'back-up', and F8 is listed as 'reversing lights' - as well as F1 in the under dash fusebox. There's actually a number of mistakes in the Haynes electrical diagrams, so only use them as a last resort.

[culzean]

Is "back-up" actually reversing light? If so is there a relay on it?

No relays, just an old fashioned switch in the gearbox. Fuse for this is in the under dash fusebox, F5 or F1, depending on early/late fusebox.

F8 (under bonnet fusebox) is described as 'back-up' in the Jazz handbook, it's a permanent live that feeds the radio, ECU, instruments, immobiliser, etc., etc..

Here's a bit of a tale though...

Just to confuse matters, if you have a Mr Haynes book, they appear to have mis-transcribed 'back-up', and F8 is listed as 'reversing lights' - as well as F1 in the under dash fusebox. There's actually a number of mistakes in the Haynes electrical diagrams, so only use them as a last resort.

'Back up' is an Americanism I suspect,  that they use instead of 'reverse'.  Don't know how the ever 'back up' their computers though,  wonder if the have to push them backwards..?

[UKjim]

I’m suffering the same problem, which I originally thought was the starter motor.


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[culzean]

The smallest wattage light bulb on the car in cabin, glovebox, boot etc  ( 5 Watt, unless you have LED bulbs fitted ) will draw about 500mA.   If the aircon relay is stuck you are looking at about 3.5 amps, any other relay stuck ( heated screen etc ) maybe 10 amps, headlight relay stuck is quite obvious as the lights stay on - but about 10 amps.  If the ignition key is out the cigarette lighter socket will be powered off,  sometimes people wire up a dashcam to continuous power supply and that is about 3.5watts or 300mA.

[UKjim]

I did a parasitic drain test today and my figure was about 55-58mA. I have a dashcam which is also wired to a permanent live for parking mode but it is set to sleep mode which means it will only fire up if it detects an event, although it will have some draw as it able to start recording just prior to the event, radio memory and immobiliser will also register something.

I am led to believe that most cars are between 20 and 70mA, so mine looks acceptable. Maybe my battery is not holding charge as well as it should be.

[Jocko]

I have a dashcam which is also wired to a permanent live for parking mode but it is set to sleep mode which means it will only fire up if it detects an event, although it will have some draw as it able to start recording just prior to the event

Your dashcam is recording continuously. It records in a loop, and if an event occurs, it saves that loop and continues recording. It cannot detect an event then decide to record from 10 seconds before that. You would need a time machine for that! Unless you have a DeLorean, that is.

[UKjim]

Of course you are correct, in sleep mode it doesn’t record UNTIL the event.

[embee]

If you have a typical 40Ah battery in your car, and it's a bit tired (age) and sitting at typically 70% charge, in reality you probably only have about 15Ah to play with before it will be effectively flat. At 60mA you're draining 1.5Ah per day, so at best perhaps 10days worth.
A battery might bulk charge at around 10% of its capacity (say 4A), so after a couple of days you'll need to run it for probably half an hour just to keep up with the losses.

I'd suggest 60mA is probably going to give you issues unless the battery is in really good condition and the car is used daily (or at least very regularly) for a reasonable time every trip.

High complexity cars with significant quiescent current drain (50mA+) usually have big batteries, 75Ah or so, and big alternators to keep up with losses. I still think of losses above 10mA as significant, maybe I'm a bit optimistic thinking it'll be as low as this.

[UKjim]

If you have a typical 40Ah battery in your car, and it's a bit tired (age) and sitting at typically 70% charge, in reality you probably only have about 15Ah to play with before it will be effectively flat. At 60mA you're draining 1.5Ah per day, so at best perhaps 10days worth.
A battery might bulk charge at around 10% of its capacity (say 4A), so after a couple of days you'll need to run it for probably half an hour just to keep up with the losses.

I'd suggest 60mA is probably going to give you issues unless the battery is in really good condition and the car is used daily (or at least very regularly) for a reasonable time every trip.

High complexity cars with significant quiescent current drain (50mA+) usually have big batteries, 75Ah or so, and big alternators to keep up with losses. I still think of losses above 10mA as significant, maybe I'm a bit optimistic thinking it'll be as low as this.

Thanks for the info. My battery after a full charge reaches 93% of it’s capacity and CCA is 305 against a spec of 330, do you think that’s good enough?

[culzean]

Terminal voltage is the key to battery health, it is actually like testing the Specific gravity of the electrolyte electrically ( and specific gravity is everything to a lead acid battery ). After charging you need to let battery stand for at least an hour,  but preferably longer.  I charged my 5 year old motorcycle battery yesterday and checked the voltage this morning,  it was a touch under 12.4 volts.  Now that may sound OK for a 12volt battery,  but a fully charged 12volt battery is 2.21 volts per cell = 12.65 volts.  12.4 volts is around 70% charge, and anything under 12 volts is real bad news, I am waiting for my new battery to arrive, and I will try to be as surprised as everyone else when the engine 'turns over much faster'..... ( which it always does and people are always surprised ). 

[embee]

.... I am waiting for my new battery to arrive, and I will try to be as surprised as everyone else when the engine 'turns over much faster'..... ( which it always does and people are always surprised ).

I think I'm like you in that I don't "do" tired batteries. They are consumables, like tyres, they wear out. If it's a few years old and showing signs of becoming tired, I get a new one. Just like new tyres on a bike always feel great, that smugness of prodding the starter and it bursting into life with gusto is always satisfying.

[t0m]

Quiescent current should be single figures milli-amps.
I've seen relay actuator coils draw 100+mA, check every light switch (fog etc) is in the off position.
I've also see USB adapters plugged into an aux socket draw 120mA with nothing actually plugged into them.

The other thing which caused someone grief was one of the insurance black-boxes plugged into the OBD socket. The first one was taking around 50-60mA, the replacement sent by the insurance company was around 10mA, which is tolerable.

Since you are able to measure the draw with your equipment, I'd continue with disconnecting things. Is "back-up" actually reversing light? If so is there a relay on it?

Blew the fuse in my multimeter so had to wait for a replacement to arrive before I could continue with this. I double checked all the light switches were off, nothing connected to cigarette lighter socket, no alarm fitted, no insurance black box. Current draw is still 110-120mA.

As Sparky Paul says, the "back up" circuit is permanent live to keep radio presets and ECU data even when the car is off. This got me thinking that something on this circuit is drawing too much current and I suspect it is the radio. Last summer my toddler posted some coins in to the CD slot. I managed to disassemble the radio to retrieve them and everything still worked afterwards so I thought that was job done. I wonder now if something was damaged/shorted in there?

All the radio wiring under the dash seems intact and moving the cables didn't make any difference to the current draw. I pulled the connector off the back of the radio and the current dropped to zero. Unfortunately this is clearly just breaking the "back up" circuit as the car won't switch on accessory power (position I) with the radio disconnected. So I think the only way to test if it is the radio is to replace it... Not sure what my options are on that front so I will update when I've made progress.

[UKjim]

Quiescent current should be single figures milli-amps.
I've seen relay actuator coils draw 100+mA, check every light switch (fog etc) is in the off position.
I've also see USB adapters plugged into an aux socket draw 120mA with nothing actually plugged into them.

The other thing which caused someone grief was one of the insurance black-boxes plugged into the OBD socket. The first one was taking around 50-60mA, the replacement sent by the insurance company was around 10mA, which is tolerable.

Since you are able to measure the draw with your equipment, I'd continue with disconnecting things. Is "back-up" actually reversing light? If so is there a relay on it?

Blew the fuse in my multimeter so had to wait for a replacement to arrive before I could continue with this. I double checked all the light switches were off, nothing connected to cigarette lighter socket, no alarm fitted, no insurance black box. Current draw is still 110-120mA.

As Sparky Paul says, the "back up" circuit is permanent live to keep radio presets and ECU data even when the car is off. This got me thinking that something on this circuit is drawing too much current and I suspect it is the radio. Last summer my toddler posted some coins in to the CD slot. I managed to disassemble the radio to retrieve them and everything still worked afterwards so I thought that was job done. I wonder now if something was damaged/shorted in there?

All the radio wiring under the dash seems intact and moving the cables didn't make any difference to the current draw. I pulled the connector off the back of the radio and the current dropped to zero. Unfortunately this is clearly just breaking the "back up" circuit as the car won't switch on accessory power (position I) with the radio disconnected. So I think the only way to test if it is the radio is to replace it... Not sure what my options are on that front so I will update when I've made progress.

If you are thinking of replacing the radio, why not take the opportunity of updating it to a modern double din with CarPlay or Android Auto? I have just installed an excellent unit from Amazon which performs really well and looks so much better. Have a look at my post in the ‘in car entertainment’ section.