So my car seems to live in a constant 'low battery - start engine' state and I've decided to look into it.

In a nutshell, my ctek charger charges main battery up to about 12.69V but the car only gets it up to about 12.5V and the voltage drops at up to 0.2V per day hence constant low voltage.


This is a MY14 2 battery non stop/start model with a Lion AGM 95Ah main and an Exide (LR branded) AGM 70Ah auxillary. Both batteries were fitted to the car (ie may not have been new batteries and I think not) for me when I bought it in March to solve the low battery message which then went away for a few months. I do mostly short journeys and not a lot of them.

I now have a BM2 battery monitor fitted to each so can see what is going on. The BM2s report charging at about 14.49V on both batteries. The auxillary battery seems to get itself a little top up charge each time the engine is run and settles down at about 12.9V after that and drop about 0.3V over 5 days.

The main battery charges all the time the engine is running but once switched off voltage drops to around 12.4V and then continues to drop at up to 0.2V per day. A recent journey of about 55 mins ended at 12.43V, break for lunch then journey home but still only 12.44V. I called the AA out after this whose machine pronounced the battery fine but needed charging!

Took battery out of the car today and ctek'd it, bulk load phase only so about 80% charged and now nothing connected to it at all and checking occasionally with multimeter.
Results are: at time of disconnect 13.10V, +1hr 12.63V, +2hr 12.61V, +3hr 12.59V, +4hr 12.58V, +5hr 12.57V, +6hr 12.56V

This is my first L405 so don't know what I should expect so does this look like the battery, a drain problem or BMS or what??? To me it looks like the battery is not charging fully and voltage dropping too quickly but what do I know? Chris

2014 FFRR 4.4 SDV8 Autobiography Barolo Black
2012 RRS SDV6 HSE Baltic Blue
and before I saw the light:
2011 Suzuki Grand Vitara SZ5
1998 Ford Mondeo V6 Ghia X
1990 Citroen BX GTi
1973 Triumph GT6

Hi, sounds like your main battery is getting weak and can’t hold charge, hence the messages. A decent battery fully charged shoul read about 12.6V and hold that for several days in storage. Search “Battery” on here, there are loads of threads, some with links to a cheap but decent battery capacity tester.  “If it ain’t broke, don’t fix it” -where’s the fun in that?

I'm no expert, but if the voltage is dropping like that with nothing connected, it certainly seems like an issue with the battery.

If it's already out - and you have another car - I'd take it to Halfords or Euro Car Parts and ask them to test it.

Also, as advsed on other posts, check tailgate operation is not sluggish, its a good sign of a weak battery  “If it ain’t broke, don’t fix it” -where’s the fun in that?

The main battery that I took out of the car acted like that one. Was told by a dealer that it just needed charging. I also charged it after I replaced it (to keep it for spare if was OK). But the voltage dropped quickly.

My new main battery only dropped 0.14V in 7 days while parked in temps of -8C to 4C. I am happy that I replaced it.

I think that the second battery masked the state of the main battery. SDV8 AB MY 2020
MINI Cooper S Cabrio
Kit: Jaguar XK140 (in progress - the website is link to build)

Thanks guys, I think we're in agreement that i need a new one.

Gremlin500 wrote:

.. a cheap but decent battery capacity tester.

Alistair wrote:

If it's already out - and you have another car - I'd take it to Halfords or Euro Car Parts and ask them to test it.

That would mean going in my wife's 1.0L 3 cylinder VW Up and it's back in now anyway so locked and alarmed but I will take it and see what they can tell me that I can't find for myself. Chris

2014 FFRR 4.4 SDV8 Autobiography Barolo Black
2012 RRS SDV6 HSE Baltic Blue
and before I saw the light:
2011 Suzuki Grand Vitara SZ5
1998 Ford Mondeo V6 Ghia X
1990 Citroen BX GTi
1973 Triumph GT6

luxmoggy wrote:

The main battery that I took out of the car acted like that one. Was told by a dealer that it just needed charging. I also charged it after I replaced it (to keep it for spare if was OK). But the voltage dropped quickly.

My new main battery only dropped 0.14V in 7 days while parked in temps of -8C to 4C. I am happy that I replaced it.

I think that the second battery masked the state of the main battery.

Quote:

So the second one seems to do more than just the documented help with starting.

Having had Lion batteries in cars I’ve bought before, I’d never have another again. They don’t last 5 minutes in my experience.

If you’re having issues, the first thing I’d do is bin that battery but that’s just me

David. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior