Flat Car Battery Issues

Forums › Transport (cars, bikes and boats) › Flat Car Battery Issues

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636 posts

Ultimate Geek

#3369916 2-May-2025 13:42

richms:

Disconnecting from the car is important if you are doing any desulphate etc pulse charging, as otherwise the capacitance of all the stuff in the car and over voltage shunting will mean at best nothing happens to recondition, and at worst you burn out the over voltage protections in your ECUs etc. Chances are small on a little plug in charger, but the giant buzz boxes that put out absurdly high voltages to get 60+ amps into a battery so you can crank it after its been on charge for a minuite will see over 20v on the terminals which is gonna harm things in a modern car.

this is a good point. however, i doubt any modern, so-called smart charger will pump the voltage all the way up to 20V. for this kind of thing, it probably doesn't matter whether it's a small, portable charger or big, wall-mounted one. it has to do with the charging algorithm and accurate monitoring during the process.

not that i've bothered to check, and also because i've only done it twice on 2 separate cars, ctek's recondition indicates charging to 15.8V. that level shouldn't cause any grief to car electronics.

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outdoorsnz

670 posts

Ultimate Geek

#3369925 2-May-2025 13:49

Back to my car battery issue. OK so can confirm after visit to my auto spark (plug HDLAUTO Harrex Downing & Little Ltd) that issue is not the battery.

There is parasitic load of quite high 3.2 AMPS! Will take car back next week to get this sorted. Car now parked up with negative terminal off.

So for interest sake, how do you test for this correctly? When I tested, I had disconnected bat negative, and on my very old DSE multimeter plugged red lead in the amp fused (not 10 A un-fused) and left negative plug as is, then connected in series between battery neg and car lead neg. The reading did show 32 briefly but then settled on .01

johno1234

2695 posts

Uber Geek

#3369930 2-May-2025 14:05

outdoorsnz:

Back to my car battery issue. OK so can confirm after visit to my auto spark (plug HDLAUTO Harrex Downing & Little Ltd) that issue is not the battery.

There is parasitic load of quite high 3.2 AMPS! Will take car back next week to get this sorted. Car now parked up with negative terminal off.

So for interest sake, how do you test for this correctly? When I tested, I had disconnected bat negative, and on my very old DSE multimeter plugged red lead in the amp fused (not 10 A un-fused) and left negative plug as is, then connected in series between battery neg and car lead neg. The reading did show 32 briefly but then settled on .01

I would just disconnect one battery terminal, then complete the circuit with your ammeter - assuming it has a overcurrent protection fuse. 3.2A or 40W is a lot! Equivalent to having brake lights or all interior lights or similar on. I'd leave the ammeter on then start pulling out and in fuses until it drops.

nitro

636 posts

Ultimate Geek

#3369988 2-May-2025 14:27

outdoorsnz:

So for interest sake, how do you test for this correctly? When I tested, I had disconnected bat negative, and on my very old DSE multimeter plugged red lead in the amp fused (not 10 A un-fused) and left negative plug as is, then connected in series between battery neg and car lead neg. The reading did show 32 briefly but then settled on .01

wonder if you've blown a (DMM) fuse. that other terminal usually has a 200mA limit.

if you get it showing the 3.2A parasitic drain, start disconnecting the fuses (the car's) one at a time until you find the one that clears the current drain.

richms

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#3369989 2-May-2025 14:28

There are many modules in a car that sit across that power and just go to sleep when the car is idle. They have capacitors that will charge and then they briefly wake up do their thing and go back to sleep. This is why you basically cant charge a dead battery when its in the car with a small charger, as the voltage comes up, things wake up, draw more current than the charger can supply and then it drops. This happens a few times and then the little maintanance charger will error out and not do any charging.

I know a couple of people that also bought the cheap small ctek to put on unused cars and have found the car battery dead and the charger flashing error after leaving it for a month or so. They are not put it on and forget about it things and I am a little annoyed that noone seems to be making an IoT car battery charger that lets me keep an eye on it.

I did get some bluetooth battery monitors off aliex to put on the unused cars but they seem to make it run flat about 4x faster and the app is a piece of crap that needs you to be in range of the unit when it does its periodic broadcast to have a chance of seeing that its starting to get low.

Richard rich.ms

tweake

2296 posts

Uber Geek

#3369991 2-May-2025 14:35

if you have an accurate meter, you can test volt drop across the fuses. that can narrow down the circuit involved.

tho first i would check for things like interior lights that don't go off when the door closes, including the boot light. check if you have any non-switched cig sockets with something plugged into them (phone charger, maps, dash cams, etc)

tweake

2296 posts

Uber Geek

#3369993 2-May-2025 14:38

outdoorsnz:

Back to my car battery issue. OK so can confirm after visit to my auto spark (plug HDLAUTO Harrex Downing & Little Ltd) that issue is not the battery.

There is parasitic load of quite high 3.2 AMPS! Will take car back next week to get this sorted. Car now parked up with negative terminal off.

So for interest sake, how do you test for this correctly? When I tested, I had disconnected bat negative, and on my very old DSE multimeter plugged red lead in the amp fused (not 10 A un-fused) and left negative plug as is, then connected in series between battery neg and car lead neg. The reading did show 32 briefly but then settled on .01

one of the problems is when you first connect a battery, all the ecu's and modules charge up. so you get a burst of current at the start. i hope that didn't fool the auto sparky.

richms

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#3369995 2-May-2025 14:51

Also it can be boot or glovebox lights, record a video on your phone and put it in them and close it and see if it goes off or not.

When a friend had a draw problem it was his amps not going to sleep because some water had got in between the positive and the turn on lead for the amps and they were never turning off. Not the sort of thing you would really notice unless you were to watch the lights on them when not using the car. Under the seat was not the best place for them in an old car with shot seals too.

Richard rich.ms

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#3370004 2-May-2025 15:12

richms:

My concern is that you are going straight from a stop to full load with no chance for the oil pressure to come back, and noone can explain what magic they have to prevent bad wear when hitting high loads as soon as its started.

It seems to be a problem for BMW (they admitted it and changed the coating of their rod bearing thingy), but why it's not a problem for the gazillion Toyota hybrids I have no idea.

richms

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#3370012 2-May-2025 15:20

Batman:

It seems to be a problem for BMW (they admitted it and changed the coating of their rod bearing thingy), but why it's not a problem for the gazillion Toyota hybrids I have no idea.

Probably because they all drive like gravety is the only form of acceleration available to them and just roll away from the green light watching the giant display to check their efficiancy stats are still all good.

Remember that all the manufacturers care about is that the car outlasts warranty coverage. A change to get better effiicancy that will have the engine totalled out and the car an economic writeoff at 150000kms is a good thing for them. They have zero incentive to make these things operate in a way that is not detrimental to the life of the car.

Richard rich.ms

nitro

636 posts

Ultimate Geek

#3370021 2-May-2025 15:44

richms:

I know a couple of people that also bought the cheap small ctek to put on unused cars and have found the car battery dead and the charger flashing error after leaving it for a month or so. They are not put it on and forget about it things and I am a little annoyed that noone seems to be making an IoT car battery charger that lets me keep an eye on it.

not sure i've seen a "cheap" ctek, pricewise. i think they're priced at a premium. especially as they are rebranded Lamborghini, Mercedes, McLaren, Porsche, etc.

interesting feedback on what you (your mates) have experienced. of course, without having all the information, they could have been aged batteries that reached eol. they seem to be good enough for Jay Leno, but i don't know if he's getting paid by them!

iot charger? likely just a matter of time. ctek and victron have models with bluetooth connectivity in the market already, wifi shouldn't be too far behind - assuming there is a sizable market for it.

richms:

I did get some bluetooth battery monitors off aliex to put on the unused cars but they seem to make it run flat about 4x faster and the app is a piece of crap that needs you to be in range of the unit when it does its periodic broadcast to have a chance of seeing that its starting to get low.

not sure i understand this correctly. the medium is bluetooth. how else is the app going to receive the "broadcast" if not in range?

anyway, a battery monitor that drains the battery! 😂

Asteros

192 posts

Master Geek

#3370029 2-May-2025 15:55

richms:

I know a couple of people that also bought the cheap small ctek to put on unused cars and have found the car battery dead and the charger flashing error after leaving it for a month or so. They are not put it on and forget about it things and I am a little annoyed that noone seems to be making an IoT car battery charger that lets me keep an eye on it.

In my experience Ctek chargers perform very well. I bought mine in NZ and it came with a 5 year warranty. They are set and forget. Agree errors usually come from a battery that needs to be replaced.

richms

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#3370030 2-May-2025 15:56

nitro:

not sure i've seen a "cheap" ctek, pricewise. i think they're priced at a premium. especially as they are rebranded Lamborghini, Mercedes, McLaren, Porsche, etc.

interesting feedback on what you (your mates) have experienced. of course, without having all the information, they could have been aged batteries that reached eol. they seem to be good enough for Jay Leno, but i don't know if he's getting paid by them!

iot charger? likely just a matter of time. ctek and victron have models with bluetooth connectivity in the market already, wifi shouldn't be too far behind - assuming there is a sizable market for it.

The cheapest in the range that is only a maintainer and not a charger. 1A or something rating which they listed as being suitable for maintanance of a normal size car battery. That seems to be a lie.

Also with their more expensive ones, there is no way to just have it jump straight to the put craploads of power in mode like with other chargers. I have had better luck keeping cars outside full with just a cheap solar panel, until it rusts leaks and all corrodes away accelerated by the battery voltage.

nitro:

not sure i understand this correctly. the medium is bluetooth. how else is the app going to receive the "broadcast" if not in range?

anyway, a battery monitor that drains the battery! 😂

Yes, but if you are in range some of the time but not at the right time, you miss its transmission - the phone doesnt connect to it on demand when present near it. When the car is running you get live data and it will let you know about voltage drop when cranking and chargeing voltage etc, but for something that you walk past twice daily when its idle, its hopeless to get an alert about it getting low.

Also there are concerns that its sending your location data back to China. I did look at if there was a way to get the data on an ESP Home ESP32 that I could chart them and alarm based off it, but no viable outcomes present.

Richard rich.ms

outdoorsnz

670 posts

Ultimate Geek

#3370033 2-May-2025 16:00

tweake:

one of the problems is when you first connect a battery, all the ecu's and modules charge up. so you get a burst of current at the start. i hope that didn't fool the auto sparky.

No he gave it a good 10 mins to allow for all of that.

tweake

2296 posts

Uber Geek

#3370036 2-May-2025 16:12

outdoorsnz:

No he gave it a good 10 mins to allow for all of that.

if its drawing that much it should make it easier to track.

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