First things first. If you think that you've got a battery problem, don't start running straight to Halfords to get it checked, try and isolate the problem your self. Can you hear the starter motor solenoid clicking when you turn the key?
Start by by-passing the supposedly faulty battery and simply clamp some jump leads from another vehicles battery terminals (with their engine running and maintaining steady revs) to the leads in your battery compartment with your battery still in place. Give it a few minutes to excite the chemicals and create a little charge and then turn your engine over on the key. It should fire straight up. Has it? If you hear a clicking sound when you turn the engine over, that's the starter motor solenoid crying out for more amps. So check that all the connections on the battery terminals / jump leads are good and clean and then ask your fiend to really rev their engine whilst you turn the key.
If not, keep your friend their with their engine running and connect a length of wire from the positive terminal of their battery directly to the spade connector on the fuel solenoid which is located on your injection pump. Then, with the jump leads still connected between the battery in your landy and the battery in their motor, turn the engine over again. If it hasn't spun up into life then there may be a couple of other problems:
1) No fuel reaching engine
2) Air in fuel line
3) No air reaching cylinders
Very slightly slacken the bleed nipple / nut on the very top of your fuel filter housing. It may have a couple of fuel pipes running into / out of a banjo ring attached to it. Find the fuel lift pump on the drivers side of the engine and then manually pump the lever. It should pump fuel up from the tank and into the filter housing. Observe the slackened bleed nut for diesel. if it bubbles, you've got air in your system. If it seeps pure diesel with no bubbles, there is no air in the system and the problem lies somewhere else. Try turning the engine over again following some manual fuel pumping, it may have helped any air through the system.
Another possibility is that you have a jiggered lift pump, which would show similar problems to what you're describing. The pump lever on the cam may have worn or bent rendering the pump useless, or the none-return valve inside the pump may have failed, allowing fuel to escape back away from the engine. If this is the case, the injection pump will be trying to draw fuel through the system, maybe from as far back as the tank, which is a lot of pumping! So be patient and keep letting it turn over (on the jump leads) until the bugger fires up!
See how you get on with that
-Pos