Monday, May 23, 2011

Charging a battery or jumpstarting a car

One thing that I do frequently is end up charging a car battery or jump starting someone's car. Frequently this is because someone let a vehicle sit for a long time (probably a month or more), or they left the lights on. Every once and a while it is because of an actual failed battery. I also charge up my wife's car every few weeks since she only drives about 2 miles a day so her battery never gets fully charged unless I do it and I charge the car battery when changing oil. When it comes to charging a vehicle's batter there are right and wrong ways of doing it which I will discuss below. As a side note if you have a limited use vehicle I highly suggest getting one of those solar trickle chargers that sell for about $20 just plug it into the 12V outlet (cigarette lighter) and put in on the dash. I use one in my Bronco II and that thing will sit for a month consistently and still starts without issue.

Jump starting a car:
I suggest carrying around a good set of jumper cables. Good ones have real heavy clamps and are at least 6 gauge wire 4 gauge wire is better (lower gauge is thicker wire).
  1. Move the running vehicle so that it's battery is as close to dead battery in the other vehicle as possible
  2. Leave the vehicle with the good battery running
  3. Make sure all accessories (lights, radio, etc.) are off in the vehicle with the dead battery
  4. connect the red cable to the red (+) terminal on the vehicle with the dead battery
  5. Connect the other end of the red cable to the red (+) terminal on the running vehicle
  6. Connect the black cable to the black (-) terminal on the vehicle with the dead battery
  7. Connect the other end of the black cable to the black (-) terminal on the running vehicle
  8. Do not attempt to start the vehicle with the dead battery yet, it probably won't start and if you do try it will only take longer.
  9. Go sit in the running vehicle for a few minutes. I suggest bringing the engine up to a faster idle (1500 RPM) so it will charge the dead battery faster. To do this just lightly press on the gas pedal, you will hear the engine speed up some
  10. After 5 or so minutes have someone else go and try to start the vehicle with the dead batter. Keep the running vehicle at the faster idle.
  11. If the vehicle with the dead battery started continue to step15
  12. If the vehicle with the dead battery turned over (tried to start) but didn't start go to step 9
  13. If the vehicle with the dead battery didn't turn over go to step 9 but let it charge for 10 minutes
  14. If you get here and have tried starting the other vehicle and it won't start the battery is probably totally dead so go get a new one, or the starter is the problem and go get a new one. Continue to step 15 and disconnect the jumper cables.
  15. Disconnect the black cable from the car that has been running the whole time
  16. Disconnect the black cable from the car that got the jump
  17. Disconnect the red cable from the car that has been running the whole time
  18. Disconnect the red cable from the car that got the jump
  19. If the car that got the jump is now running have them take it for a drive for at least 30 minutes to get the battery charged back up. Highway driving is better as that is at a constant speed and will charge the battery quicker and will put less of a load on the battery. You can end now
  20. If the char that got the jump isn't running check the battery and starter. (This will be discussed in another post later)
Using a battery charger (also applies to connecting battery boosters)
  1. Do NOT have the battery charger plugged into the wall
  2. Connect the red cable to the red terminal (+) on the battery
  3. Connect the black cable to the black terminal (-) on the battery
  4. Plug in the battery charger
  5. Select the type of charging. Some chargers don't give you an option, these are trickle chargers. The various options are below
    1. Trickle charge (1-2 amps)  This is the best way to charge a char battery, use it if getting the vehicle started can wait several hours (overnight)
    2. Quick charge (5-20 amps) This is used to quickly charge a battery, expect to let it charge for several minutes (10-30 depending on battery size and output of charger)
    3. Start (50-200 amps) This is used to start a vehicle. You should still let charger charge the battery for a few minutes (5 is probably plenty). This is really hard on batteries
  6. Let the vehicle charge
  7. Unplug your charger
  8. Disconnect the black cable from your battery
  9. Disconnect the red cable from your battery
When I charge a battery when changing oil I use the trickle charge setting on my charger. My charger is a 2/10/50 amp charger. I also use the trickle (2 amp) setting when charging my wife's car overnight.


  1. Nice and comprehensive guide, but I have one thing to add. I driver's ed, we were taught that an explosive gas (Oxyhydrogen) may be generated in Lead/Acid batteries (like the one in your car).
    If you're really unlucky, the spark from attaching the last lead on any battery will ignite it.

    The solution is to replace your step 7 above. In stead of attaching the last clamp to the battery itself, attach it to some unpainted metal part of the engine compartment (the whole chassis is electrically connected to the - pole of the battery), away from the battery itself.

    Keep up the good blogging!

  2. This is really doubtful but is something I have heard before but can't find any evidence of it happening, nor does science back it up.

    To create the explosive gas mixture of hydrogen and oxygen you need to be passing a current through a solution of water with some electrolyte in it, the process is called electrolysis. If you have a dead battery that battery isn't producing any oxygen or hydrogen as there is no current flowing through it until you make the final connection. Now this may have been a very remote issue years ago but with today's sealed lead acid batteries there really isn't a place for the hydrogen to escape from (there is but it is through the vent hose that leads outside your car). There is an issue with charging a batter in a non ventilated area because the hydrogen gas can build up and be ignited by a spark but then you wouldn't have this problem until the dead battery was connected. Another issue with this is that the sparks you are seeing are 15 volts which are very low energy (your spark plugs produce voltages in the 1000s or 10,000s of volts range) and would have a difficult time igniting anything let alone the hydrogen gas that isn't being produced yet. Even thought hydrogen is very volatile (will ignite in concentrations between 5% and 95%) it is also very light and rapidly floats away. Also you won't be able to see a hydrogen flame very well as most of the light it produces is in the UV range and the visible light is very faint and in the blue to violet range. If there really was a danger of igniting hydrogen escaping from a car battery then that same danger would exist when installing a brand new battery, and I don't ever hear about exploding batteries at auto factories or when people install new batteries themselves since both of these also produce those same low voltage sparks.

    I have heard of batteries that were damaged internally exploding when on a charger or while being jumped. This is usually caused by over charging the battery, or by there being an internal short between the plates.

    As far as attaching to an unpainted metal part in the engine bay that may work, but I have had problems on older vehicles as the grounding becomes questionable as rust builds up on connections and metal parts (even aluminum oxidizes). Rust, like all metal oxides, is a really good insulators. So finding a good clean piece of metal with a good ground can be difficult.

    My experience has been that most high school teachers aren't anywhere near as knowledgeable as they think they are. I had one tell me that it took more energy to recycle aluminum cans (melt them down into an ingot) than it takes to create new aluminum (mine bauxite, grind it up, electrolysis out the aluminum, and then melt it in to an ingot). This was only the most glaring example there were numerous others.

  3. There are times when my car battery has died good thing that there is another car around to jump start me.
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