Battery voltage query

[ianess]

2 batteries on my long laid-up vehicle were both dead.

Charged 1 up and got engine started and left ticking over for a couple of hours.  Next day...no start but BOTH batteries reading 8.5 volts on test meter.

Can anyone explain what`s happening?

[sddsddean]

Normally tickover is not fast enough to put a decent charge in a battery. If your tickover is about 600 rpm, you need to set the revs to at least 1000 rpm to get a decent charge.

[madgeezer]

battery drain? my old metro use to drain batteries like christmas toys due to faulty glove box light not switching off. and also i drove a lot at night and the alternator was broken therefore not charging the battery. you can check this by putting ur foot down and putting the meter on the terminals of the battery (if it doesn't go up then ur alt is dead).

[honkytonkman]

Batteries work best when they're constantly discharged and then recharged. Ideally a battery that's not going to be running a car for any length of time should be trickle-charged periodically. In the dim distant past I had buckled battery plates on a vehicle that was laid-up for a long time and although a powerstart got it going, I had to buy a new battery.

When starting a car the battery is almost exhausted hence the recommendation to run a car at least 10 miles for each start up. So even a seemingly decent battery will fail to kickover a cold engine.

A totally flat battery that is eventually coaxed to start a car will never charge up to full capacity from driving about.

[ianess]

Thanks for that, madgeezer........reving the engine makes no difference so it looks like a charging problem.

  The joys of motoring!