Flat Car Battery Issues

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2695 posts

Uber Geek

#3370862 6-May-2025 10:07

Bung:

It will depend on publishing date. The MXS 5 instruction video is 7 years old now. The video that mentions BMS is 1 year old. The car used in the video isn't identified but could be a VW clone. Not something I'll run into 😁

It's the same in the current PDF you download from CTEK.

If the post is connect to the battery + and the battery - is connected to the chassis and engine then there is no electrical difference. The physical difference is spark proximity to the battery vents.

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nitro

636 posts

Ultimate Geek

#3370906 6-May-2025 12:35

tweake:

however i doubt that connecting to a post would be an issue. the main thing a bms does is to stop draining the battery to much and to monitor/control charge rate while driving. it would check battery voltage on startup and go from there regardless. domestic plug in chargers are not big enough to cause an issue.

some of them (bms) apparently track the charging cycles the battery has been put through, via the alternator or otherwise... as well as the type of battery to ensure proper charging, also considering the age of the battery.

tweake

2296 posts

Uber Geek

#3370910 6-May-2025 12:44

nitro:

some of them (bms) apparently track the charging cycles the battery has been put through, via the alternator or otherwise... as well as the type of battery to ensure proper charging, also considering the age of the battery.

yes, you have to input battery specs into the ecu when you replace a battery. a charging cycle by a home charger is negatable. i suspect its really only concerned with the very rapid charging done by the alternator which can be damaging to the battery. a home charger should be low enough not to effect battery lifespan.

this brings up a good point about having high amp battery chargers charging small batteries. either get a small charger or use a adjustable output charger. we have a quite a few chargers because some are for bikes, some cars, utes, tractors etc.

tripper1000

1604 posts

Uber Geek

#3370938 6-May-2025 15:54

outdoorsnz:

200mA fuse is blown, but that could have happened some time ago.

So I tried putting black in common (MM) and red in 10A unfused (MM) and completing the circuit, but still got some numbers like 36 that jumped around briefly and then showed 0.01A.

Would blown fuse prevent correct reading?

No, in 95% of multi-meters the high current 10amp range works fine with a blown low current fuse. However if someone overloads/connects an unfused 10A range wrong it can damage/kill the 10A range.

If you mistakenly select AC amps you usually see an initial reading that rapidly returns to zero. So just confirm you have it set to DC amps (= style symbol) and not AC amps (~ symbol).

harlansmart

416 posts

Ultimate Geek

#3371236 7-May-2025 16:18

Using VCDS etc the stupid STOP/START feature is easily disabled on VAG vehicles.

richms:

johno1234:

The stop/start battery on our Touareg finally gave up after an incredible 12 or 13 years old. I wish I could remember what brand it was but it was likely to be the factory original as the car was only 2 years old when we bought it. It's a huge, very expensive battery and a pain to replace as involves removing the front passenger seat to access it.

I can't stand the stop-start feature. It is hard on batteries, ring gear, pinion and starter. Worst of all, the engine decides to conk out just when you need to hoof it into a gap in the traffic. It's almost a reflex reaction to hit the deactivate button when I start the car. As far as I can tell it can't be re-programmed to default inactive instead of default active.

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.

You can get little wiring looms that connect to tbe button and have a microcontroller that will see if its on or not and press the button to turn it off every time. Some modern cars are a ritual to get going with turning them on, turning off lane keep assist, agreeing to the stereo being a stereo, turning off start stop, and my friend in the UK has got a car now that has a speed warning nag that needs turning off every time. Sounds like something that a resoursful person could make a OBD2 module to automate.

johno1234

2695 posts

Uber Geek

#3371240 7-May-2025 17:07

Good to know! Next time I am getting it serviced I'll ask if he can toggle it.

outdoorsnz

670 posts

Ultimate Geek

#3373491 15-May-2025 11:22

Update. Turns out the car has a faulty alternator! Back drawing current. Alternator was hot as. Car engine cold.

2003 car. So finding one is going to be tricky in NZ. Bit peeved, as I hardly driven it and haven't even used a full tank of fuel yet!!!

tweake

2296 posts

Uber Geek

#3373501 15-May-2025 11:39

outdoorsnz:

Update. Turns out the car has a faulty alternator! Back drawing current. Alternator was hot as. Car engine cold.

2003 car. So finding one is going to be tricky in NZ. Bit peeved, as I hardly driven it and haven't even used a full tank of fuel yet!!!

just pull the alternator out and go get it fixed. very rarely need to replace alternators.

richms

27982 posts

Uber Geek

Trusted

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#3373503 15-May-2025 11:47

Its usually the diodes in the alternator that fail and cause that to happen. Should be an easy repair for most auto sparkies that do alternator reconditioning.

Richard rich.ms

nitro

636 posts

Ultimate Geek

#3373510 15-May-2025 12:04

getting it fixed would likely be better than swapping it out for something from the wreckers - won't know what state those are in. as mentioned, most car sparkies do this routinely.

Batman

Mad Scientist
29691 posts

Uber Geek

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Lifetime subscriber

#3373564 15-May-2025 12:21

tweake:

outdoorsnz:

Update. Turns out the car has a faulty alternator! Back drawing current. Alternator was hot as. Car engine cold.

2003 car. So finding one is going to be tricky in NZ. Bit peeved, as I hardly driven it and haven't even used a full tank of fuel yet!!!

just pull the alternator out and go get it fixed. very rarely need to replace alternators.

My autosparky said fixing a 15 year old alternator costs the same as replace with new. So we did that

tweake

2296 posts

Uber Geek

#3373572 15-May-2025 13:01

Batman:

tweake:

just pull the alternator out and go get it fixed. very rarely need to replace alternators.

My autosparky said fixing a 15 year old alternator costs the same as replace with new. So we did that

what was the cost? and was it oem replacement or a cheap copy?

Batman

Mad Scientist
29691 posts

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#3373585 15-May-2025 13:51

tweake:

what was the cost? and was it oem replacement or a cheap copy?

you know that OEM is not what you think it is nowadays?

the current lingo indicates that OEM mean not original. Original Toyota is "genuine" OE is genuine minus Toyota logo. OEM might as well be a copy. (it used to be different but now OEM apparently has been diluted to copies.)

mine was not OE or Genuine Toyota regardless. was it cheap? probably. who pays for expensive stuff if the cheap one works just as well.

IIRC it was between $300-400.

is OEM as good as repairing 15 year old OE?

I will tell you that OEM new comes with product and workmanship warranty. OE repair does not.

tweake

2296 posts

Uber Geek

#3373586 15-May-2025 14:00

Batman:

tweake:

what was the cost? and was it oem replacement or a cheap copy?

you know that OEM is not what you think it is nowadays?

the current lingo indicates that OEM mean not original. Original Toyota is OE. (it used to be different but now OEM apparently has been diluted to copies.)

OEM is a copy. mine was not OE regardless. was it cheap? probably. who pays for expensive stuff if the cheap one works just as well.

IIRC it was between $300-400.

is OEM as good as repairing 15 year old OE?

I will tell you that OEM new comes with product and workmanship warranty. OE repair does not.

OEM = original equipment manufacture ie toyota or bosh etc.

they must have come way down in price. used to be $300-400 for a copy and often $100-150 to repair. tho repair cost can vary. i did have the clutch go and it was one of the most expensive ones you can get.

outdoorsnz

670 posts

Ultimate Geek

#3373707 16-May-2025 11:08

The issue with older cars now, is actually sourcing parts either new (after market etc) or 2nd hand.

I've been told anything over 10 years is now hard. So I decided to first get car back home and use local mechanic. As sparky rightly said, we could take alternator to bits, and if can't get parts, you are stuck...

Will see what options we can find. I'm also mindful of something relatively simple becomes quite expensive!

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