Have an unbranded lead-acid battery charger and a small 6Ah 12V battery. After about a year of purchasing the set I need to charge it for the first time. For car battery jump start I vaguely remember needing to reverse polarity of charging cable. In case of charing my little battery here what is the polarity to keep in mind while setting it up for charging?


closed as off-topic by Leon Heller, Daniel Grillo, Matt Young, placeholder, tcrosley May 13 '14 at 14:18

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    \$\begingroup\$ The question is a bit confusing because I've never heard of a reason why you'd want to reverse the polarity while jump starting a car. But for charging what is presumably a SLA battery you'd just connect positive to positive. \$\endgroup\$ – PeterJ May 13 '14 at 12:19
  • \$\begingroup\$ Thanks PeterJ. Will need to check the source of where something about deliberate reverse polarity was suggested. I tried to search casually, but didn't find the reference -- which indicates that I might have been mistaken or misunderstood the jump-starting procedure. \$\endgroup\$ – icarus74 May 13 '14 at 12:34

You DEFINITELY do not reverse polarities when charging.

  • Connect +ve to +ve (usually red jumper lead)

  • Connect -ve to-ve. (usually black jumper lead)

Doing it the other way round can damage the battery and/or the charger.
If connecting batteries together with jumper leads, a reversed polarity connection can lead to a battery exploding. An exploding wet battery can throw acid.

For long battery life most batteries will benefit from being charged more often than yearly. Battery capacity is slowly lost overtime and as voltage falls sulphation can occur.

Batteries are best not charged at a very high rate.
This is too complex a subject to deal with in a few lines but, as a guide, keeping charge rate below about C/5 is sensible. With a basic charger you may not be able to control or monitor charge rate. For this sort of application other factors will probably have the major effect on battery life and improper charging rate is probably a minor nail in the coffin of battery lifetime.

Battery University
Charging lead acid batteries

Lecture: Lead-acid batteries ECEN 4517/5517.
EECE Colorado Interesting

Powerstream Charging basics

  • \$\begingroup\$ Thanks for the tip-off regarding more frequent charging. \$\endgroup\$ – icarus74 May 13 '14 at 12:35

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