Old Car Battery

[WoodlandsCamper]

I have a car battery in the garage that I haven't used for over 10 years. It was bought new at the time and only used to power a strip light in our tent camping days. The multimeter gives a reading of zero volts, as does the smart charger (which also gives an error symbol because it's below 3 v). Is it safe to try and recharge the battery or is there likely to be an explosion? There are flush caps on the cells although the label says the battery is 'maintenance free'. Any sensible advice welcome?

EDIT: The reason I want to resurrect the battery is because daughter's car had trouble starting this morning.

 

[Sproket]

WC

I had one the same a few years ago, and to get the charger to work i put a pair of jump leads from another battery and let it self equalise for about an hour or two, by that time the dead battery was showing about 7volts and the charger worked, most chargers will cut out if they sense a very low voltage. i then connected a headlight bulb to drain it back down & then re-charged it, ( after about 5 times ) the battery was back to about 50ah ...

If it don't work you haven't lost anything only a bit of time ....

 

[WoodlandsCamper]

I've just put the battery on a dumb charger set to trickle charge. The reading on the multimeter started at 10.15v and the last digit is increasing by one about every 1 minute, so there may be something going into the battery.

 

[ProfJohnL]

Hello Woodlands,

There are others on the forum with a better detailed knowledge of battery construction than me, but what I do know is that car batteries have a plate construction which is more of a mesh. The mesh is filled with a lead based paste, and normally it should remain sticking to the mesh, but when its discharged for a long time, the paste starts to break away from the mesh. When this happens the battery is beyond simple recharging.

If you have been luck and the paste has remained attached to the meshes, then with careful regenerative recharging the batter may come back to life, but it is likely to have reduced charge capacity and the peak current it can handle will also be down on new spec and might not be enough to start a car.

I would be surprised if the old battery works on your daughters car, but if it does its not likely to last very long. But it might worth trying provided you daughter is staying close to home where you can *** out with jump leads if she gets stuck.

As Sproket suggests you haven't got anything to loose.

 

[jay1976]

whats up with daughters car might be better off sorting that out in case it lets her down away from home.. sounds like her battery is past it if its struggling to start

 

[Woodentop]

The best way to bring a battery up is to charge it at constant current rather than constant voltage as used by most chargers. In the likely event that you do not have one it can be equated by using a higher dc voltage source - say 48V or more - and putting a suitably rated resistor in series with it. Such a resistor is called a headlamp bulb.

Failing that if you have a power supply such as is used in a caravan with 13.8V at 20A available, connect it to the battery in series with a flasher bulb. The bulb will shine and limit the current and as the battery comes up the bulb will get dimmer and dimmer until it goes out. At that point the bulb can be taken out of circuit and the power supply connected direct to the battery.

Smart chargers are good and effective but only on an initially healthy battery. Very smart chargers - that cost an arm and a leg - will recondition the battery by trickle charging with large current pulses superimposed. They are the best but at a price.

As someone else said, the simplest solution is to jump it to a known good battery for a couple of hours, then use your charger.