Charging Leisure Battery?

fast is easily ok but can reduce battery lifespan by breaking down electrode plates if done to often and long. slower charges are better for a longer lasting life of battery though it will make no difference to a batteries capacity to store energy.

use a trickle charger ideally or even a solar powered one to keep it topped up between uses . a battery left discharged can and does reduce its own capacity to store energy ( plates sulphate up) whereas a fully charged battery can last for over a decade if treated correctly.

If a battery is allowed to become fully discharged it will usually reach a state where resurrection is impossible, which is what I suspect has happened to yours. As already said, you should also be using a purpose-built charger.

always better with slow charge if you have the time .sometimes fast charges destroy cell life ok .only use fast in emergancy . caravan owner.ok. all the best .

better for the battery to slow (trickle) charge for longer life.

best way to charge a batery is by getting one of those pulse chargers