Battery drops to 8 volts on startup, need a new one?

[Supergumby5000 5,000+ posts]

i have a cheap 2/6/10a black & decker battery charger that has an alternator tester on it, maybe he has something similar that would help

where can i pick one of these up? the only real autoparts store we have in town is napa.

 

[Moe Lester 10+ year member]

where can i pick one of these up? the only real autoparts store we have in town is napa.

dont bother, you have a volt meter. turn the car on and see what voltage is present at the battery when the car is on. if it is steady around 13.5 or higher it is going to keep the battery charged.

 

[CRXBMPN 5,000+ posts]

wal mart for like $29 and its come in handy on many occassions... just real nice to have a battery charger handy.

 

[NeverEnuffBass 10+ year member]

Before you go buying a new starter, be sure to check all the connections on it first. I made that mistake once only to find out it was a loose cable

 

[audiobahnuser18 5,000+ posts]

Well bro it could be a number of thing's.

Here's some thing's it could be

1.) Could be the alternator is not charging the battery which is making the voltage low like that.

2.) The starter could be bad , pull the starter the gear should only spin one way.

3.) The battery is bad one cell could be sulfated or the battery itself just needs a charge and is low.

4.) Bad Connections.

 

[AlpineUser 10+ year member]

sounds to me like something may be left on which is causing the battery to slowly go dead...there is a test you could do to see if it is that but you need to find your oem specs for it and then do like 11 other steps...its called a parastetic draw test ...i spelt the p word wrong i know that but we just did this in electrical class at school

 

[ShiningBuick 10+ year member]

Sounds like what happened when my batt died.. Like the one guy said, it's supposed to stay above 9.6V upon startup.

If you have a really good digital multimeter you'll have a probe to measure amps that goes by magnetic field that you just clamp around the wire you want to measure amps in. If you've got the luxury of having one of those measure your various wires.. started wire should pull 150-250 if I remember right, and the alt sohuld be putting out around 100 with all the accessories turned on, maybe a little more little less, and also keeping the system voltage between 13.75 and 14.75V.

If you've got a load tester run a load test, and load it till it pulls 1/2 the battery's CCA, and hold it for 15 secs. the voltage should stay above 9.6 there, too, and if it dips below it's no good. If it dips below that just starting I'm guessing your battery will dip way below 9.6 at an even higher load for 15 secs.

If you're still looking for nifty things to test, make sure you're not dropping voltage over the various high-amperage circuits. Test voltage drop between the alt and battery, should be below .4V. Voltage drop should be below .4V on the pos and neg side of the started circuit, too. Make sure to measure all the drops while under load (cranking or heavy charging)

Sounds like the batt for sure though.

 

[jdawg 5,000+ posts]

If its at 8v you are probably screwed. Letting it idle wont charge the battery anyways, sometimes turning the headlights on will pull enough current fot the alt to charge though. I had a car that hadnt been started in 6mths, let it slow charge at 5 amps for a day and a half. Been fine since. In fact im working on it for inspection and it sat for 2 weeks after that and it started right up.