Car wont start after drive, runs fine battery 25%

[SuperFast]

6 Amp charge, manual charger (6A/2A Schumacher brand unit) charging now. had to go buy charger

Charger showed 25% when i put it on there. seems it was ok for a few weeks, sitting included, now i go for a 30 minute spin, all is well. Go to start car, battery is low ? (turned wouldnt start)

i bought a 6 amp and 2 amp manual charger, selectable. its charging at 6 amps now. I will purchase a multimeter next

please tell me how i can best diagnose the health of this battery, and multimeter will also tell me if alternator is charging it as it should. passed store diagnostic test

its a sealed cell battery with no caps

Im most interested in "letting it charge overnight" on 2A, but i can NOT read that triangle on the charger ! its complicated epecially at 2A triangle is way small.

 

[Food Scientist]

Let it sit overnight on 2 amps and take it to a parts store and test the battery with a load tester. This will tell you real fast if the battery is any good. You can get a cheapie mulitmeter at Harbor Freight for about 5 bucks.

 

[NateDN10]

Look at the voltage across the battery terminals when the car is idling, when you've just shut it off, and after it's been sitting for a while.

At idle, you want 13.8 - 14.4V; when the car's off you want at least 12.5V.

 

[PeteTheFarmer]

You can use the multimeter to test the battery's voltage at rest and while being charged by the alternator, but to to a load test which is important you need another tester or take it somewhere which has this tester. Usually Advance Auto or Autozone does this for free. Otherwise, you can do a poor man's load test by cranking the car with the headlights on to see how dim they get.

 

[SLCraig]

Originally Posted By: PeteTheFarmer
You can use the multimeter to test the battery's voltage at rest and while being charged by the alternator, but to to a load test which is important you need another tester or take it somewhere which has this tester. Usually Advance Auto or Autozone does this for free. Otherwise, you can do a poor man's load test by cranking the car with the headlights on to see how dim they get.


Poor man's load test for the win.
Why remove the battery if you don't have to?

You may still have to, but that may tell you all you need.

 

[The_Jeff]

When you first put a battery on a charger it has lower internal resistance so it's going to take the full 6 amps for a few minutes. Though this shows as "25% charged" you have to return after 1/2 hour to see what the needle settles down to.

If you can somehow rig the multimeter up to read volts while you're starting you need at least 9 or 9.5V. Beware digital multimeters jump around every 1/2 second and it's hard to get a good cranking reading. Harbor freight has as good a multimeter as anyone and they're only $4 right now. Also you can get a "dwell/tach/volts" meter at practically any thrift store; everyone used them in the 1970s and earlier and they're obsolete now... except for the volts portion.

I'd just seek out a new used junkyard battery. Go for Johnson Controls, they have octagon shaped vent caps and easy to read date code stickers. And they don't go to pot that much.

 

[lewdwig]

Originally Posted By: SVTCobra
Let it sit overnight on 2 amps and take it to a parts store and test the battery with a load tester. This will tell you real fast if the battery is any good.


+1

 

[Eddie]

+2 Let it charge for 10-12 hours at 2 amps.

 

[wrcsixeight]

12 hours at the 2 amp rate will return 24 amp hours into the battery, not including inefficiencies.

His battery probably has 60 to 70 amp hours.

12 hours might allow the battery to start the engine, but not enough to fully charge it.

Use the 6 amp setting. The low and slow approach on a very dim battery is no longer a great idea.

Low and slow is good when the battery is 80% and above and you have all the time in the world