how do i know if?

[xcrocx]

can anyone tell me how can i tell if the alernater is working or not as this morning my battery was flat so i bought another one, i dont know how long its been in the van (which is a 2lt diesel) i did leave my lights on about a month ago and had to jump start it, could that be the trouble?. also can i charge the old one up so i've got a spare and carry it with me in the van?
thanks in advance . croc

[tony]

you need to buy a simple mutimeter,get your van running put the lights on and connect the meter across the battery,if it shows 12volts or less the alternator is not working.
12volts to 13 volts its working but not very well
13 volts to 14 volts all is well the problem is somthing else.
14 volts + theres a problem with the alternator ,and it needs replacing.

[xcrocx]

tanks tony