If you’re pushing a manual car with a flat battery BACKWARDS, do you put the gears into Reverse or Neutral? Also, are there any specialist firms who visit you to replace batteries, but aren’t necessarily a breakdown service?
If you're hoping to push-start it, it needs to be in gear.
However, I'd be pushing it in neutral backwards to somewhere that I could then push forwards in gear.
1)Neutral
2) Halfords do a home visit and fitting service. Some other National Auto centers do offer similar services.
RAC also do supply and fit at home, you do not need to be a member.
If you're trying to push start a car you need it to be in a high gear otherwise, when you release the clutch, it will stop dead. Reverse is a very low gear, so just about impossible to bump-start it by pushing, so take ginge's advice and push it in neutral to somewhere you can push it forwards and use 3rd or 4th gear.
You need a bit of momentum to push-start so the vehicle needs to be moving with the car "freewheeling" until you attempt to turn the engine through the gears - the free movement can be either in neutral or in gear with the clutch depressed (the latter is easier for a sharp/immediate cut/grip of the clutch). If the car is moving forward (pushed, pulled/towed or down an incline under gravity) then 2nd gear is possibly the best to try, if it is moving backward then it must be in reverse gear. The ignition must be on. If the engine is warm it may only need the slightest and very brief turn to start (ignition and fuel feed being good, problem if not). If it is cold and especially if the ambient temperature is low then it may need a "proper" lengthier turnover. It is better if the clutch can be released and then depressed quickly/very soon with you ready to rev the engine a bit (not loads) than to aim to drive off directly on/from the start-up - this is especially the case going in reverse.
I have started a car(s) in reverse this way and I always use 2nd gear unless I can build up something faster than brisk walking pace/speed. Whether 2nd or third depends on the car's gearing ratios but the higher the gear the slower the engine will be turned when you release the clutch. First gear is, in most cars, too low because the engine's resistance has too much effect.
If jumping from another car, make sure you connect and disconnect from your battery correctly- google jump starting- and don't run the doner cars engine while cranking yours.
Halford will probably charge you an arm and a leg to fit a battery at your home address. (They're currently running radio ads offering to fit batteries at their stores "from £15", which is outrageous when you consider that they tend to charge more for batteries than many smaller companies do and, in particular, that many other auto parts stores will do it for free!)
If you've got a good local mechanic (particularly one who you already give business to) it might be worth giving him a call. I know that the guy who fixes all the problems on my car probably wouldn't charge me a penny for driving the half mile to my home and fitting a battery which he supplied to me (at a very competitive price too).