Alternator Testing?

The warning light is an integral part of the charging circuit on some designs - hence if the bulb is blown you may not get the correct charging voltage from the alternator. So check/replace this first. You need to work out the charging current of the charger (written on the charger) and the capacity of the battery (written on the battery.) If you're trying to charge a dirty great van battery from a weedy little car charger, you may be there a while. However, if your battery is badly sulphated, you will never get a high reading on the hydrometer as much of the acid is permanently combined with the lead plates.

That's worrying/interesting - lead acid cells are 2v by their nature, so something's a bit strange here. I'm intrigued - can you tell me what sort (make/code) it is, so I can look it up.

All i can tell you is my friend obtained it from a local farm machinery shop, the outer two caps seem to be a resivoir for the battery as they have no plates in them, it is made by chloride and is AH276 Industrial battery the other specs ive already supplied, hope this helps.

it is blue someone sugested it is a leisure battery for a caravan

Thanks - that's a bit clearer. If it doesn't have plates, that doesn't count, it's a six-cell battery. Don't quite understand why it would have 8 caps, I'll see if I can find out. BTW it's not a leisure battery, leisure batteries don't have CCA figures, they are designed for full cycle use i.e. complete discharge/charge at a reasonably slow rate. Vehicle batteries are designed for continual charge, occasional rapid discharge.

When you say 'tractor' battery, are you sure you don't mean 'traction' battery. These are used in milk floats, and golf buggies etc, and are really unsuitable for vehicle use.

Could it be a NiFe (Nickel Iron) battery? Uses an alkaline electrolyte (potassium hydroxide) and is 1.2volts/cell. Less likely damaged by deep discharge than Pb/H2SO4 batteries but lower energy density and more expensive, although this is offset by a longer working life. IIRC should also be charged like NiCd's (i.e. at constant current not constant voltage).