batttery re charge time after one start

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Impossible to say without knowing the parasitic load on the battery during that week.

Getting a Lead acid battery from 80% charged to 100% charged takes about 3.5 hours on a healthy battery at higher absorption voltages, 14.4 to 14.8ish volts.

The more charged a battery is, the slower it charges.

I have an AGM battery which when absolutley stuffed full, accepts 0.0x amps at 14.7 volts. The X is because i have no ammeter which can read currents to this small level

If I start my vehicle with this 100% stuffed full battery, when the amps required to maintain 14.7v taper back to 0.0x amps, the battery can again be considered fully charged.

This takes about 45 seconds. This proves not that the battery recharges quickly, but that very little of the battery capacity is requred to start a modern fuel injected vehicle.

a 0.05 amp parasitic load is 1.2AH of capacity each day taken from the battery

A car battery is generally 65 to 85 AH capacity.

Voltage is electrical pressure, HIgher pressures cause more amps to flow, but a 80%+ charged battery can only be recharged so quickly, and this rate is pretty slow.

Best to always have a lead acid battery at full charge. Anything less is detremental to some degree.
 
It usually takes my car 5-10 miles to 90% recover from a start at highway speeds. Idle is not going to charge much. When I start it the voltage goes up to 14.5 and starts to taper. After a good 45 minutes it is down in the 13.7 range. Depends on the temperature too as hotter will be lower voltage.
 
Originally Posted By: Donald
With EFI and an engine that has been tuned up the current drain for one start is minimal.

The cars I am familiar with turn the starter for fraction of second before the engine catches. The current drain for one start is indeed minimal.
 
wrx has the "right answer" but I'll append that if your battery is only at 80% you'll get back where you started (pardon the pun) faster than if it was at or close to 100%. Discharged batteries with lower internal resistance take more amps at a given float voltage.

Temperature compensation keeps your battery from boiling dry; cars go up to 14.5 volts after starting to wake up their cold batteries with lethargic chemistry. They drop to 13.8 not because the battery is full but because it (or the alternator) is warm.

Dodges use a battery temp sensor while other cars infer temp from alternator temp or a body control module program. Some drop the voltage to 13, "neither charging nor discharging" to save fuel. I would bet nearly every car "puts it back" within the first minute, probably because of clumsiness sensing the rising heat level and temporarily "overcharging", which I put in quotes, as it's a matter of opinion (luck?) unless you have an ammeter on the battery cable seeing flow in or out.

The only other possible nail in the coffin is if your car has air-ride suspension, smog air pump motors etc that run after startup and would consume all of the surplus amperage.
 
My dad told me once in the 70's that one start and you need todrive 15 minutes to put that back into the battery. No clue if that was/is true.
 
Originally Posted By: shokhead
My dad told me once in the 70's that one start and you need todrive 15 minutes to put that back into the battery. No clue if that was/is true.


It depends ENTIRELY on the voltage regulator set-point, and % of alternator output available.
 
If a vehicle is going to sit for more than a week, say two or three weeks, should a Batt Tender be hooked up?
I use a Tender on the tractor and riding mower in the fall and winter when it sits for long periods, but often my
truck will sit for two or three weeks and I've not been putting a Tender on it.
 
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The issue with battery charging on modern cars is not recovering from a start, it would do that in the first half mile. A bigger problem is when you wake the car up by opening the door there are any number of computers drawing current and that adds up to several amps. It's the same when parking up as the car takes several minutes to go to sleep. You can't open a door or the boot lid when the car is parked in your garage without triggering a draw of several amps and it doesn't stop directly the door is closed again. For these reasons it's not possible for a modern car to finish a journey and start the next journey with a 100% fully charged battery even before thinking about leaving it for a week. A battery tender is certainly in order.

O for the days when opening a door just turned on the interior light.
 
A tender is a good idea but so are solar panels, especially if your cigarette lighter is always on.
 
I picked up one of these solar battery chargers on Amazon a month or so ago and it works great. It will easily keep a battery topped off and manages to charge my bikes battery a lot quicker than its 7.5w rating would suggest. The pathy has a moderate parasitic draw and after a week the battery would read 12.34v with the solar charger only getting a few hours of direct sunlight a day it is now in the 12.67-12.7v range


HIGHLY recommended

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O for the days when opening a door just turned on the interior light

I can't resist. Please forgive me " Especially anything with Lucas* electrics and wiring.

*Lucas, AKA, the prince of darkness. Former owner of a very decrepit XJ6
grin2.gif
 
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Originally Posted By: SilverFusion2010
How tough is that solar panel? Could it survive being rained on and otherwise living on the hood of a car?

I leave it on the roof of the Pathfinder and so far its been ok in very light rain but I would not want to get it soaked. The cells are protected by translucent plastic.
I park 400 feet away from my front door and do not want to lug around a 60 pound battery back n forth just to put it on a charger. This is the best option I have for keeping the batteries topped off.

The one improvement I would make is longer power leads. They are about half as long as they should be imo but it was fixed by some splicing.

Its been the best 20 bucks I have spent in a long time.
 
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