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Charging another car with the Miata

My brother's Honda Civic has a possible alternator problem when he got stuck. I replaced his battery with a new Sears Diehard around 3 days ago and he drove it a short distance to his parking space where its been sitting unused.

On Monday, I plan to convoy along with my brother over to a Honda specialist around 5 miles away. I'm guessing that the new Sears battery has lost some power just sitting unused for 3 days. The weather has not been very cold, around mid 20s to mid 40s. Even though the battery is brand new, I don't want any problems driving the 5 miles on Monday.

A friend recommended that I charge my brother's battery, in the morning, from my Miata just to top it off.

What is the best way to do this? I've never done it before. Should I just connect the jumper cables and leave his car NOT RUNNING, but with the Miata RUNNING. Approximately how long should I charge it? BTW, my battery is not an original OEM battery. Its the after market one that most people purchase.

Reply to
Pat
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Unless there is a short somewhere, I wouldn't think that a brand new Diehard battery would lose it's charge in three days of non-use. It should start the car without needing a charge.

Pat wrote:

morning,

Reply to
DBLZOOM

I was thinking more about after its starts, and just topping it off. If you don't use the heater, fan, off, and lights off, will a new battery get the car 5 miles without first charging it up a bit?

Reply to
Pat

You're worried that if, in fact, the alternator is the problem that the car will be driving strictly off the battery? It's a good concern. Quick test - if the headlights normally get brighter on the Civic with the car running (as opposed to with engine off), and they don't now, then yeah - there's probably an electrical issue with the charging system. Or, if you had a multimeter, just measuring across the battery with the car running it should be above 13V normally instead of 12 when the engine is off.

The idea of starting his car off your battery isn't a bad idea, since the initial engine turnover is a huge momentary drain on a battery that the alternator usually "tops off" again over a short time (if the alternator is working). But after the engine starts, the current demand goes down considerably - especially with all the ancillary items off as you're thinking. I think he'll make it (but it's good you'll be following him, as it's not the traveling distance but the traveling time that potentially would cause a problem). I would probably do as you're thinking and start the car with the jumpers in place, although his battery will still take the larger brunt of the engine turnover current demand, due to resistance in the cables. That should be enough "support" for the battery though.

NW

Reply to
Nordic Wally

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