Battery 'Good' - yet not full charge..?

GoldenShadow

I have a Fiesta Titanium (2009). It has powerfold mirrors too.

Yesterday morning, the car unlocked but mirrors didn't fold out until I started the engine. Today, my radio had turned off, air con gone to factory settings, time and date to factory settings, wiped my milage trip to 0 etc.

I accidentally rant he battery flat in Dec (left dash cam plugged in for four days). Between then and now it has been fine (post jump start of course!).

Went to Halfords. They tested the battery and said it is good, the only issue is the max capacity is 480 and it was at 430. They did say it wont ever be 480 but should be closer than 430 really. They said go for a 10 mile drive and it should go up, but I then explained I had already done 40 miles to get there and they said hmmmm maybe buy a charger and charge it up overnight.

They didn't seem too confident that that would fix it. Could that be it? Ford have quoted me £70 for half an hour of diagnostics...

Does anyone have any idea what it might be?

Strider590

I don't know what your messing about for, just get a new battery for god sake.

All you can do is change things and hope the issue goes away, the battery is an easy and cheap place to start. If you let it run flat as in deep discharge, then it's probably going to give up next winter anyway.

Kids at Halfrauds don't know what they're doing anyway.

pappa_golf

"they said hmmmm maybe buy a charger and charge it up overnight."




what a good idea , the charging of the battery overnight , not buying tat from them


do it , over weekend , a nice low but long charge , simply expecting it to fully recharge after being flat and bumpstarted , is asking to much

pogofish

If its an original battery from 2009, then it has had a decent innings and a new item from a car parts supplier should cost you less than the "diagnostics".

IME a failing battery can often give you contradictory test results anyway and even if passing, it could still die on you the next time it is put under load or when the temp starts to drop.

AdrianC

"480" and "430" are going to be cold cranking amps - the maximum amount of power the battery can put out in one go.

That's nothing to do with capacity - which is measured in amp-hours, and would be somewhere around 60Ah for a typical smaller car battery. The capacity is what stops the battery going flat quickly. And it can't easily and quickly be measured, except by flattening the battery - and flattening a battery is one of the best ways to reduce the capacity and kill it.

£70 of diagnostics is getting on for twice the price of a new battery...

As far as your battery going flat goes, it sounds like either something's sucking a lot of power overnight (Boot or glovebox light staying on? Some electronic guff not going into power-save as it should?), or the battery's pretty damn dead.

forgotmyname

The battery is weak either replace it or cross your fingers each time you want to start it, especially as the winter comes. Thats when you will really notice it.

I always recommend a good overnoight charge with a 6 - 8 amp charger.
Minimum of 8 hours, do that every couple of months in the summer and monthly
during the winter to help the battery live longer.

arcon5

Why can't they load test the battery?
And voltage check alternator?

Take it to a proper garage!

Joe_Horner

As usual, all the completely non-MSE advice to "just buy a battery" is missing one very important clue in the OP, so I've made it a bit more visible below:

GoldenShadow wrote: »

Yesterday morning, the car unlocked but mirrors didn't fold out until I started the engine.

A battery that was so low on voltage that it couldn't operate the mirrors, or that lost the stored data in ECUs would NOT have enough power to start the engine.

Especially the ECUs are far more dependent on voltage than current to hold data, and they'll generally hold it down to around 10 volts - they have to because battery voltage can dip to that cranking on a cold morning while the starter's running.

But a battery that had dropped to 10V or below overnight simply wouldn't crank the engine in the morning.

Therefore, not a battery problem. Possibly a battery connection problem but more likely to be a poor earth somewhere in all that modern electronics which is depriving some electronics of voltage while allowing it to the starter because that's using a different earth.

bigjl

Cars can play up when the battery is weak.

Current Jaguars are particularly prone and the car will start but all kinds of spurious issues and fault codes will manifest themselves.

Either a proper overnight charge or a new battery are the only options.

Once a car battery has been flattened it will never fully charge from the Alternator, that is not the function of an alternator.

The fact the battery was fine till something was left on to drain it would push me to charging the battery first, as you will be able to keep the battery charger for many years

Strider590

Joe_Horner wrote: »

As usual, all the completely non-MSE advice to "just buy a battery" is missing one very important clue in the OP, so I've made it a bit more visible below:



A battery that was so low on voltage that it couldn't operate the mirrors, or that lost the stored data in ECUs would NOT have enough power to start the engine.

This isn't true, in the 8 years I owned my Vectra the battery failed twice and each time the first signs of failure were the car starting but the dash not working at all.

A battery can start the car, but if the voltage drop during starting is too great, it'll play havoc with the electronics.

Joe_Horner

Strider590 wrote: »

This isn't true, in the 8 years I owned my Vectra the battery failed twice and each time the first signs of failure were the car starting but the dash not working at all.

A battery can start the car, but if the voltage drop during starting is too great, it'll play havoc with the electronics.

Agreed, but in the case of the mirrors they'd "played up" (failed to extend) before starting so it wasn't down to voltage drop from the starter.

And if the battery was too weak to extend the mirrors it would certainly have been too weak to crank the engine.