As we see so many questions regarding Batteries here is a short information sheet
1.Only 30% of batteries actually reach the 4 year period, the cause Sulphation
2.Main cause of sulphation are
2a Batteries not being charged or left to go flat
2b Batteries sit too long between charges. As little as 24 hours in hot weather and several days in cooler weather.
2c Battery is stored without some type of energy input.
3.A lead acid battery is actually classed as discharged at 11.9v not 0v
4.If you have a lead acid battery and the voltage is around 10.5v you have a cell gone down
6.If you fit a larger capacity battery you will not need to uprate your alternator, you just take longer to charge it but you have more reserve energy
7. A completely flat battery 0v will never recover its full capacity, and should be replaced
8. To charge a 12v lead acid battery fully you need to see voltage of 14,2-14.3v which is why the regulators voltage setting you see me quoting is 13.7-14.3v, once fully charged however if you then continue to charge at the higher voltage all you do is boil off the electroyte, and the term gassing comes into play.
Once fully charged you can then maintain the batttery fully charged state with a voltage of 13.4-13.6v, this state is known as float voltage. This is the reason why you dont leave your battery in your classic Mini with either a normal or trickle charger, if you want to leave your classic on charge when not in service use one similar to a Optimate Smart Charger which I use. Be aware though some smart chargers will shut down on a cycle and not cut back in until 12.5v this is to low, so if you have a classic parked up with a smart charger and ever see 12.5v when its turned on, its time to get a better float/smart charger.
Any other questions just shout someone will advise accordingly.