re: Battery Polarity

whydahdvr · Post by **whydahdvr** » Fri Jul 09, 2010 2:45 pm

Has anyone run across a situation where a battery's polarity switches? The battery in the cowl box is reading opposite when I pulled it out to recharge. The battery charger identifies a reverse hook-up so right now it's got the positive lead on the negative terminal, vice versa.
Add to that that my jeep doesn't seem to have any juice running through it either.
-Josh

hill · Post by **hill** » Fri Jul 09, 2010 3:08 pm

Yes if the battery was 100% dead and the charger was connected backwards ie.positive on negitive & negitive on positive it will charge reverse. You can discharge completly and recharge the correct way and be alright . I work in a Toyota dealership and, had experienced this before .By customers not paying attention to what they were doing .But be sure to completly discharge first.

whydahdvr · Post by **whydahdvr** » Fri Jul 09, 2010 3:34 pm

That must have been what happened, the light switch was left on and the battery cable connected so it must have drained out and then reversed. Any particular way to let it drain out completely again? Thanks.

Post by **wesk** » Fri Jul 09, 2010 8:35 pm

Connect an old head lamp parallel with it and when the lamp filament doesn't glow anymore your discharged.

whydahdvr · Post by **whydahdvr** » Sat Jul 10, 2010 3:46 am

Cool. That's what I was thinking would work but didn't want to try it without learning more. I've blown too many things up - for work and fun as well as by accident. Right now that would freak my wife out.
Thanks again!

whydahdvr · Post by **whydahdvr** » Mon Jul 12, 2010 7:04 am

Got the battery discharged and hooked up to my battery charger. Now it's again reading that it has a reversed hook-up, but the charger read a dead battery when I started. Any thoughts or suggestions?
Thanks.

Post by **wesk** » Mon Jul 12, 2010 8:14 am

Is the battery totally dead? No reading whatsoever on a digital volt meter?

Your real reversing issue may be your battery charger.

When it is totally dead connect it parallel to another battery for a short while.
Then connect it to the charger.

whydahdvr · Post by **whydahdvr** » Mon Jul 12, 2010 9:20 am

I must be equipment-challenged. After reading my digital voltmeter instructions I still don't comprehend what I'm looking at on the readings. Anyway, hooked the batteries together in parallel for a couple minutes then hooked the battery charger up and the needle went crazy. Looks like it's reading the A/C flow as it bangs back and forth.
Apparently I've forgotten everything I learned in my electrical engineering courses for my commercial dive license.
Help!

Post by **wesk** » Mon Jul 12, 2010 9:53 am

Select DC range. Place red lead on + / POS terminal and Black lead
on -/Neg terminal. If the battery is reversed in polarity you'll see a - / NEG symbol in the meter window ahead of any voltage reading.

whydahdvr · Post by **whydahdvr** » Mon Jul 12, 2010 9:59 am

Yup, did that, but what gets me is the readings for Amps. I didn't see anything for voltage but was getting -0.120 mA.
Sounds like I'm doing and reading it right after all. Thanks.

whydahdvr · Post by **whydahdvr** » Mon Jul 12, 2010 10:23 am

Seems to finally be charging properly. I must not have left the two batteries connected long enough or drained the reversed battery enough the first time around.

whydahdvr · Post by **whydahdvr** » Tue Jul 13, 2010 4:38 am

Success! It took all day to get the battery to charge up but this morning the jeep fired right up again. No more problems there!

Post by **wesk** » Tue Jul 13, 2010 9:23 am

Glad you are rolling again.

A couple of things to keep in mind when charging batteries. They are charge rate and time. The lower rate and longer time is usually the better choice. High charge rates just age the battery quicker and boil out electrolyte. The type of charger you use and it's ratings can differ widely but for 12 volt batteries in the 40 AH to 100 AH range can get by with a quality automatic charger with a 10 amp HI and a 2 amp LO (trickle) rate. If the battery is very low to dead it may take a few minutes on 10 amp to get the battery to start taking a charge but then switch right away to 2 amp and allow it to charge at least for 8 to 12 hours. Overnight is not uncommon. Invest in a device to measure the electrolyte's specific gravity called a hydrometer. Use the hydrometer to gage the success of your charging attempt.