Charging a car battery question.

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Discussion Overview

The discussion revolves around the process of jump-starting and charging a car battery, focusing on the connections made during the process and the reasoning behind them. Participants explore the concept of grounding and safety considerations when connecting batteries.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how connecting the positive terminal of a good battery to the positive terminal of a bad battery, and the negative terminal of the good battery to a solid metallic part of the bad car, creates a closed circuit.
  • Another participant confirms that the negative terminal of the bad car's battery is grounded to its body frame.
  • A follow-up question is raised regarding why the negative terminal of the good battery should not be connected directly to the negative terminal of the bad battery.
  • One participant explains that connecting to the chassis ground helps avoid sparks near the battery, which can produce flammable hydrogen gas during charging.
  • Another participant suggests following battery wires for easier and safer connections, mentioning that some GM cars have a designated positive post for jump-starting.
  • One participant prefers connecting the negative to a substantial piece of metal on the engine to ensure that heavy current does not flow through potentially weak frame wires.

Areas of Agreement / Disagreement

Participants generally agree on the grounding concept and safety practices, but there are differing opinions on the best practices for making connections during jump-starting.

Contextual Notes

Some assumptions about battery connections and grounding practices are not fully explored, and there may be variations in vehicle designs that affect the discussion.

Who May Find This Useful

Individuals interested in automotive maintenance, particularly those learning about battery connections and safety during jump-starting procedures.

perplexabot
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Hey. Was jump starting and charging a car battery a couple of days ago for the first time. I connected the positive of the bad battery to the positive of the good battery, then connected the negative of the good battery to a solid metallic, non-painted part of the engine on the bad car, or the body frame.

My question is: How is this a closed circuit? Is the negative terminal of the bad car's battery connected to its "solid metallic parts/body frame?"
 
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Yes, the negative is grounded just as you said.
 
marcusl said:
Yes, the negative is grounded just as you said.

Thank you for the quick reply. My mind is now at ease.
 
Ok now a follow up question if you don't mind. Why then not connect the good battery's negative directly to the bad battery's negative?
 
Batteries produce hydrogen gas bubbles as they charge, and this can be vigorous for a fully discharged battery. Connecting to chassis ground keeps any sparks away from the battery and flammable gas.
 
Last edited:
Thank you.
 
Follow your battery wires.
Most GM cars have a positive post near the battery for jump-starting. It'll be underneath a red plastic pop-up cover.
Sure easier than trying to grab that battery side-post terminal, and safer too as marcusi pointed out.

I like to connect negative to a substabntial piece of metal on the engine. I figure starter is bolted to engine block, so starter's heavy current doesn't have to flow through a potentially weak frame wire on its way back to my jumping battery's negative..
 

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