We commonly get asked "I left my car battery go flat, if I recharge it will it be ok ?"
As with many things battery related the answer is not a straight forward yes or no. You need to consider a few things.
1. How "flat" has the battery become ?
If you have simply left the lights/radio on overnight and the car doesn't start the next day, there is a good chance that recharging the battery fully will revive the battery to a usable state.
If the car has been left flat for a long period of time, for example a car that has not been used for 6 months, and there is absolutely no charge left (dash lights or headlights do not light up at all). It is very likely that you will not be able to recharge the battery and if you do manage to charge it, the internals would be damaged from sulphation and the battery may let you down suddenly in the near future.
2. How old is the battery ?
If the battery is over 4 years old we would normally recommend changing it if it has been left flat for any considerable time. The older a battery gets the more its performance reduces, and everytime a battery is left to go flat it reduces its performance even more.
3. How do you recharge the battery ?
If the battery is left to go very flat, it is always recommended that the battery is disconnected from the car and placed on an advanced multistage charger to recieve a full charge.
Jump starting the car and letting it run or driving it for 10 mins is not good enough.
If you plan on driving long distances or using the car daily for a commute of 30 or more minutes this might also be able to recharge a flat battery from the cars alternator, if the battery is not too old or not damaged from being left flat.
You can always take advantage of the numerous free battery tests available from retailers and fitters if you are unsure.
It is always better to be on the side of caution with a battery, get it tested and changed if necessary.
The cost, problems,dangers and grief of being stuck somewhere when you need to use your vehicle normally out weighs the cost of replacing your battery and the peace of mind that comes with it.