Bringing a Battery Back from the Dead

If you are like me, it hurts to pay big money for a little bike battery that lasts for only a short time.... most are rubbish, designed as cheaply as possible, and we have come to expect the short life they give. So much for modern technology. If they are left discharged for even a few days, they are permanently damaged, their capacity drastically reduced. Also, I have noticed that bikes without electric starting equipment have more battery woes ... lead acid likes to be worked hard. The huge current demand for the short time the bike is started, "exercises" the plates, and keeps the battery healthy for longer.
Generally, one cell will die, and after a short time, will begin to turn white inside the case. This is caused usually by Dendrites, or small needle like crystals forming between the plates, slowly shorting them until that cell will no longer take a charge. After this, the cell will rapidly begin to sulphate, and then its buggered.
However, old misery guts here, has discovered a way to revitalize most of these batteries that can give many years more service.
Firstly, totally discharge the battery by leaving the headlight on overnight. The battery MUST be dead flat. Then connect it to the battery charger BACKWARDS, yes , it will work... BUT DON'T DO THIS IN THE BIKE! The battery will slowly begin to reverse charge, and after a few hours will be fully charged but with very low capacity. Reconnect a load to it and completely discharge it once more, and repeat the reverse charging a few times more. Finally, after again discharging it completely, it can be charged in the correct direction, chances are it will now be ok. You will need a good old fashioned charger for this, the modern "clever" type are no use. The battery voltage will need to rise to around 17 volts to be effective. You are looking at the simple transformer/rectifier only type.
The theory is this.
1) The dendrites grow in one direction because of the polarity between the pos and neg plates, reversing this voltage dissolves them.
2) Lead sulphate can only form on the positive plates, and because it is a stable compound is very hard to reform back into lead. If it suddenly finds itself on a negative plate, it just doesn't like it at all, some will either reluctantly change back into lead oxide, or simply fall into the bottom of the battery case, where it will normally do no harm.
At NZ $100 for an average motorbike battery, its worth a shot.