Member Since: 24 Jun 2006
Location: Different Planet
Posts: 206
Low battery warning - understanding what is being measured
I recently had my 5 1/2 YO battery go flat, just a click when trying to start, twice within 3 days.
With battery on a 16hr charge each time with my CTEK 5.0, as soon as ignition back on, Low Battery Start Engine warnings so bit the bullet, new battery and BMS reset by local LR dealer
No problem since, no warnings.
I bench charged my old battery the same way again and after leaving it for a week still reads 12.61v.
So why would the D4 register low battery if the voltage was typically 12.6v + after charging?
Does the car just measure voltage full stop or has it a clever way of determining that there's not going to be enough battery grunt to start the car of left any longer?
I know it's not just about volts so did the car detect something I couldn't and flag up the engine start warnings.
2015 D4 HSE in Corris Grey
All below gone but still with happy memories
2010 D4 XS in Stornaway Grey
2006 D3 S in Zermatt Silver
2001 Td5 Oslo Blue
1993 300Tdi Arken Grey
19th Aug 2020 10:12 pm
M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8231
Amps provide the cranking power not volts but without sufficient volts you won’t get the amps. A fully charged battery should be nearer 13.4v, 12.6v is about 30% charged.It can when others can't,
It will when others won't,
It goes where others don't.
20th Aug 2020 7:25 am
Griffmaster
Member Since: 24 Jun 2006
Location: Different Planet
Posts: 206
I thought 30% charged was down to about 11.8 volts though 12.6 volts being 80%ish?
2015 D4 HSE in Corris Grey
All below gone but still with happy memories
2010 D4 XS in Stornaway Grey
2006 D3 S in Zermatt Silver
2001 Td5 Oslo Blue
1993 300Tdi Arken Grey
20th Aug 2020 7:49 am
thisandy
Member Since: 28 Jan 2018
Location: Pembrokeshire
Posts: 308
My theory for what it’s worth is that it’s due to the battery’s failing capacity and some parasitic drain while it was still connected.
20th Aug 2020 5:18 pm
M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8231
That level of charging is with the alternator not a smart charger, a smart charger can charge to a higher voltage than a alternator, but it is still irrelevant if the battery does not have sufficient cranking amps, to check the cranking amps you need a drop (load) test, this is something a smart charger cannot do.
I find the best indicator of a weak battery on a D4 is the SS, if the SS does not operate without a fault light the Cranking battery is down on cranking amps, if the SS does not operate with a fault light the Auxiliary battery is down.It can when others can't,
It will when others won't,
It goes where others don't.
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