How long will my battery last between charges
A Word about Batteries
Please use this as a guide, the best way to find what suits your requirements is by your own experience
If left unused for long periods, lead acid batteries tend to deteriorate, the plates "sulphate" and dramatically reduces the Amp Hour rating. A Sulphated battery will reach a fully charged state quickly but will also flatten quickly effectively acting like a much smaller battery. Charging and fattening a sulphated battery may revive it a little but full capacity will never be achieved.
Modern car Batteries
Modern car batteries are designed to provide large amounts of current for a short period of time rather than the small current for a long period as per this application. Batteries intended for caravan or emergency lighting are more suitable. As a general rule physically heavier batteries tend to contain more lead and have a higher Ah rating.
When charging a lead acid cell you should be aware that explosive hydrogen gas is produced. Never smoke or use a naked flame near a charging battery and always turn off the charger before connecting or disconnecting it. When the cells start to bubble the battery is charged and only the electricity supply company benefit from leaving it longer. Maintenance free batteries that have no holes to top up the electrolyte level should only be charged with a special charger, normal charging equipment will almost certainly cause permanent damage and possibly an explosion.
"The old car battery behind the shed, under the flower pots or in the garage probably won't be up to the job especially if it was faulty when removed from the car and has been unused for several months or years!"