Battery V alternator...

[Jeff16v]

I'll set the scene
Mkiv golf 2.0 8v gti
Battery ran flat two months ago during cold spell
Charged it up and working fine since
Until today, wife drove it home, stopped on the way and after a 35minute drive the battery didn't have enough charge to start it again. The clock reset to 0.00 so flat battery.
I jumped it and drove it home without any problems
Tested battery after turning it off 12.5v
Running at idle-13.5v
Running with everything on - 13v

Charged it indoors on the charger and it reach 13.9 then charger said charged.
Disconnected it and it's dropped to 12.6 in an hour.

The question is battery knackered or alternator.

I think charging at 13.5 is on the low side

Id be Grateful of opinions.

[Novasport]

Check the battery voltage on cranking, if it drops way below 10v replace it

[Jeff16v]

Check the battery voltage on cranking, if it drops way below 10v replace it

Thanks mate, I'm just about to put the battery back on now in the rain, will check it.

[mowgli]

how long was it on charge for?

[Jeff16v]

how long was it on charge for?
About 25/30 minutes

[mowgli]

not anywhere near enough to tell if its the battery.. it needs 12hrs minimum

[Jeff16v]

not anywhere near enough to tell if its the battery.. it needs 12hrs minimum
The problem was the battery was showing 12.5v before putting it on charge, I wanted to see what it might top out at. 12.9v was the ceiling.

I've just put the battery back on and now it's charging at 14.1v, I cleaned the battery terminals and lead ends before re-assembly. It was only charging at 13.5v before I out it back on. That might explain why the first time she stopped it started fine, but died the second time, either a dodgy earth or gunked up terminals.

The battery has one of those did windows and is lit up green which normally indicates the battery is fine, also the battery light never comes on when it's driving around.

I couldn't see what it dropped to on cranking as the multimeter lead aren't long and it dropped off the engine cover when I started, I need a pair of hands tomorrow to check

[mowgli]

you just can't rush charging a battery, & this weather makes for a lot of battery use, with heaters & wipers going more.

your little boost helped, but these newer cars have sensors that will tell the ecu if it is low on battery power & simply not let it work.

[Jon_nova1]

I'd say it was a dodgy conenction, when you placed it on charge and it dropped thats normal, the battery is 12V and it would only be a surface charge too, the fact that it "lost" its charge in 35 mins would say to me it was either driven with the charge light on or the connection had become loose (maybe from when you played with it 2 months ago)

[Jeff16v]

When I crank it over it drops from 12.5v to 6V. It just about starts.

[Novasport]

When I crank it over it drops from 12.5v to 6V. It just about starts.

That's well fcuked, time to get a new one!

[mowgli]

disconnect it & charge it properly please....

my stepdad has had a ride on mower that has been regularly charged (whilst still connected) & still needed boost starting every time it got used for 2 years.... i disconnected it & charged it overnight, and now its fine..

[Nova_Tek]

Batteries may hold 12+ volts when not used but soon as you askl them to send loads of power that's when it matters. I had a old battery that held a charge of 12.6 volts after a good 12 hour charge (topped it 's fluids up too). Soon as I tried to crank the engine it went dead.

[Jeff16v]

disconnect it & charge it properly please....

my stepdad has had a ride on mower that has been regularly charged (whilst still connected) & still needed boost starting every time it got used for 2 years.... i disconnected it & charged it overnight, and now its fine..

It's on an overnight charger in the house, I did the same thing two months ago but now the problem has come back.

I'm assuming that the alternator pumping out 14v means its fine and its the battery that has lost legs.

If the crank drops to 6v again tomorrow I'll get a new battery tomorrow.

[Jeff16v]

Charged for 24 hours, still crap

Got a new battery reserved from euros, found a code online and got 15% off, £57 3 year exide.

Got there and they didn't have it so gave me a Bosch silver for 48p more, 4 year warranty. Touch.

Fitted on car, perfect!

[Novasport]

Glad you got it sorted, the cranking voltage check always gives away a duff battery.

[Jeff16v]

Glad you got it sorted, the cranking voltage check always gives away a duff battery.

Thank for the help buddy.gotta spread the love before + you.