Jump starting, bump starting and battery chargers

Jump starting

Opinion is divided. Many owners have jump started their cars with no problems, one used the leads about ten times. But one owner says he had a blown ECU after an AA jump start (the car went flat, was jump started, then failed, then needed a new ECU at the dealer). Several others couldn't see how connecting a second 12 V source could damage anything. Theories offered, none proven:

• A voltage spike when the leads come off. One owner says the alternator on the flat car produces a spike when the load of the donor battery is removed (a "load dump"). Another says the spike happens for a few milliseconds before the regulator gets control, and happens when the alternator speed first starts charging. A third said the regulator should prevent any overvoltage, and asked for evidence.
• The remedy offered: leave the leads connected, with the donor car running, for about five minutes before trying to start. That lets the flat battery take some charge and reduces the load. One owner adds that on some trucks you keep the lead connected for around half an hour after starting.

Owners' procedure (2010 and 2014):

1. Switch both cars' ignitions off. Make sure the cables don't touch the chassis.
2. Connect to the VX first, taking care not to short the battery to the car.
3. Start the donor, then (after a few minutes, per the advice above) start the VX.
4. After starting, disconnect from the donor first, and then from the VX.
5. Run the car for more than half an hour to put some charge back.

• Reaching the battery. Lift out the washer bottle and you should get the cables in there, or use another decent earth point on the car for the second lead (one owner). See Main battery replacement.
• Safer alternatives suggested by owners: charge the battery with a CTEK or similar, or take the battery out and charge or replace it.
• Bump starting has worked for several owners with no problems, as long as the ignition lights come on. One owner finds that easier than waiting.

Chargers

• The CTEK range is the most recommended. Owners named the MXS 5.0 (about £40 in 2015) and the Multi XS3600, which one owner says gave enough charge to start the engine in just over 30 minutes. One owner says the maker gives a 5-year warranty that also covers damage to the car from mis-charging (his claim, not checked). Cheaper copies sold by discount supermarkets (about £12 in 2010) were also used successfully, as was an Oxford motorcycle charger. An Optimate or Accumate conditioner was suggested for batteries that seem dead. One owner uses an Optimate 4 with the lighter adapter.
• The 6 V rule. A Halfords charger needed about 6 V in the battery to start charging, according to its instructions as quoted. A completely flat battery made some chargers do nothing, in which case bump or jump start the car, run it for a minute or two, then reconnect the charger so the light comes on. The instructions also said batteries below 6 V will almost certainly be damaged. Another owner believes the CTEK also needs to detect some minimum voltage, and his trick was to connect the dead battery to a full one, attach the CTEK, and remove the link once it started charging.
• Dead after a long rest. One owner's battery had gone completely flat and wouldn't light the charger after nine hours, and he eventually fitted a new one. Another says a trickle charger wouldn't revive his, but a normal charger left overnight did.
• For a quick charge of a battery that is low, see the voltages in Flat battery and charging system.

Charging while it is in the car

• Through the lighter socket. Several owners charge through the cigarette lighter socket in the centre tunnel, for years without trouble, with a CTEK or a discount copy. One says the socket has a 20 A fuse, which protects the wiring. Another owner uses one of the two auxiliary sockets under the dash. One owner couldn't get a consistent connection and wired a lead to the battery instead. Make sure the plug engages tightly.
• A caution. One owner says not every charger is the same and the car's electrics have been damaged before (burned wires). If you want to be safe, make a second lead with thicker wire connected directly to the battery. Another says an intelligent charger is needed, since a plain trickle charger could damage the battery eventually.
• Permanent lead. A CTEK includes a quick-connect lead you can leave attached to the battery, which makes connecting a two-second job (called the Comfort Connect). Check the one you buy includes it. Alternatively, an owner fitted a waterproof socket under the front clam behind the splitter so he can plug in under a car port.
• Access. Another owner runs the charger cable up to the gap between bonnet and windscreen and tucks it behind when not in use. A solar charger was used by one owner in summer.
• Leaving it on all winter. Owners have done this for two to three years with no problem. But one owner has a CTEK that caught fire and says it was the unit failing, not about being covered or confined. Another owner says don't cover the unit or put it in a confined space. If you use one, extend the wires between unit and battery so the unit sits where a fire wouldn't do harm.
• Disconnecting the battery is another approach. One owner asked in 2009 whether charging with the battery still connected avoids the alarm sounding on disconnection, and the thread has no answer.