How far can you drive on the battery w/o altenator?

My wife’s 95 honda civic is having an intermittent altenator problem. She ran the battery down and it would not start last night. I charged the battery - it wouldn’t charge fully, but it started. We drove 17 miles to the repair shop. She said the alt light did not go on during the trip, it was daytime, so no lights. So is the altenator just giving enough charge for running w/o lights? I know it will need a new battery and altenator, I’m just curious.

Does the alternator light come on with “key on engine off”? The amount of time you can drive on battery only is dependant on many factors, there is not a set answer.

Automotive batteries have a reserve capacity that’s reflected in minutes. This is the amount of time the battery will supply the vehicles electricals so the vehicle can continue to run in the event the charging system should fail. So for example if the battery has a reserve capacity of 90, it’ll supply power to the vehicle for an hour and a half before the battery is depleted.


It is possible, in this case, that the alternator is providing a less than full charge to your battery. I have not found the alternator light to be a really good indication that the alternator is performing properly. At least two alternator replacements never had the alternator light come on at all. Better to check actual charging current at the battery with engine running than to believe the light.

The fewer the amount of accessories that are turned on the more time you should have to run the engine. As for a firm answer to the distance I don’t think anyone can give you that since it depends on a number of factors like battery condition and other such things.

I suggest you get a load test done at a shop to verify the condition of the charging system and battery.

With my first diesel, I could drive until it got dark or the battery died. My current diesel will go a long time, but not forever.

How far would depend in part on the battery you have. I have an heavy duty battery, but not has heavy duty as some others.

Many auto part stores will check the condition of your battery and charging system for free. I suggest you start there.

My 59 t-birds “generator” gave up the ghost 3 hours from home. Luckily it was during the day and made it back without any problems. You may go longer than what the reserve capacity of the battery is, as that is rated at a 25 amp draw for so many minutes so depends on what electrical components are being used.

I probably could of went another couple hours as the car still started strong after making it home as reasons being, only draw on the battery was the ignition which measures at 4 amps, fuel pump and radiator fan are engine driven so only used about 12 amp hours out of the battery.

On newer cars the battery has to supply the ignition, fuel pump, computer, electric fans etc so time is shorter.

You refer to that alt. light not being on but it better be on when the key is turned to the RUN position and the engine has not been started. If it is not the alt. will never charge and one would hate to replace a number of things when it may not be anything more serious than a burned out light bulb.

Thanks for all the really prompt replies! The guys on this forum are always a great source of help. The alt light was on when she was driving last night, but as I said not today after I charged the battery and driving in the day time w/o any lights etc. on. So my take is that the alt is producing enough voltage to supply the ignition system but not much else, and the battery might have gone dead if the 17 mile trip today had been longer. On my charger the needle got down to about 3 amps but didn’t look like it would get to zero, the battery is not new. I always figured that an alternator would either charge or not charge, but not just charge a little. This misconception may come from my time in a parts store where the ‘diodes?’ would fail in the alternator, and I never thought an alternator could charge less than normal but enough to run the car. Thanks again, I really appreciate the information.

If your battery is fully charged you can run about an hour on the battery before it has too little power to keep the car running. Lights and blower fan running will shorten the time.

In the daytime, a lot longer than at night but it could cause smog system failure that can be really expensive.

You might also check the fusible link located between the battery and alt. All of the alt. current passes through this link and with age and overheating the link can start to break down.

I think the one on this particular model is an 80 Amp link and should be one of the little square deals with the clear plastic top on it. If it is, look at the wire inside of it and note if there appears to be a tiny drop of solder on one end, or both. This can be a sign of the link losing contact when it heats up.

Man you post some bizzare stuff, what is the idea behind this one? Now you have people thinking they will damage their emissions system if they drive with a charging system issue at night.