New battery...

[S3Paulo]

My S3 has been stood for some 6 weeks whilst awaiting repairs so when it came to starting her up the battery was as flat as a pancake. The garage gave it one of those 10 minute booster charges which got it away but I suspect just about did my ageing battery to death. After a short run it completely failed to start, not even a click from the solenoid. The rev counter and speedo spun round crazily and my radio when switched on, went on and off.

Anyways...Nice RAC man got it going again and I got home. Went out in normal car to Halfrauds and bought one of those £90 Ni/Cad batteries...wow what a difference....loads of spinny spinny and pow instant start. Everything operating normally too...what a bonus.

I am wondering if my past hot engine 'failure to start' moments can be blamed on a failing battery.... any thoughts...?

Thanks Paul.

[GreenV8S]

Running a battery flat is very bad for it, a healthy battery can lose 20% capacity and it is also easy to lose a cell completely due to an internal short. If the battery is completely flat then even if everything is healthy, a short trip probably won't put enough charge in to start the engine again. You need to put in somewhere in the region of 100 Amp-hours to fully charge it, which will typically take about ten hours of driving assuming ample alternator capacity - if you drive round with the headlights on, heater blasting away etc it may hardly be charging the battery at all. You don't need to fully charge the battery in order to start the car again, but even if you only put in 20% of the charge you're talking about driving for hours not minutes.

One other thing to consider - if the old battery went flat because of a fault on the car, the new battery may be OK for a while but will eventually go the same way.

[F908 Tim]

Had to do the same the other day as mine was going down and down every morning until I was on a prayer it would start at all.
A new calcium battery was £65 with 3 year guarantee,but I did need to buy a battery strap to keep it secure.
Turns over a treat.

I did hear somewhere you need to drive 30 miles to recharge what you expend in one engine start!

I do nowhere near that in a day and its my only car, with the lights on all the time,it was bound to go this winter.

[jons_s3]

Sometimes a cold snap can finish them off, but it's worth getting the alternator checked (just use a voltmeter on the battery - I think it should read around 14V with the engine running if the alternator is OK). It may also be advisable to get the system checked for drains on the battery. I've just had mine done (cost about £15).

[S3Paulo]

GreenV8S said:

One other thing to consider - if the old battery went flat because of a fault on the car, the new battery may be OK for a while but will eventually go the same way.

Yes that had occurred to me too so I put a voltmeter across the terminals with engine running and got a healthy 14.2 volts.
Of course my voltmeter on the dash only reads 13 volts.
Oddly enough,the old battery had started to bulge at one end, which can't be right.

Fitting the new one was a joy because it was a tad larger than the old one so now has a yellow lazzy strap hooked around it...looks a treat...not.

Also the terminals were the other way round...the positive reached it's post ok but the negative strap was not long enough which meant yet another trip to Halfords.

Anyways, been out in it today...goes a treat...much better with four wheels

Thanks for your thoughts chaps....Paul.