Another thing about batteries

  Covergirl 12:19 11 Oct 2011

Rechargeables always seem to come partially charged.

As I understand it, in order to get the best performance and life out of a rechargeable battery, they should be fully charged then fully discharged for a couple of cycles, then discharged occasionally if not discharged during normal usage.

So receiving the battery partially charged and giving it a full charge would theoretically reduce the life of the battery as it would need discharged before its first full charge? But one has to follow the instructions.

Am I being a bit pedantic here?

  sunnystaines 13:05 11 Oct 2011

my samsung only charges up to 80% not 100% to increase life of battery.

no idea of the logic behind it. Perhaps someone can explain to us.

  Aitchbee 15:25 11 Oct 2011

I regularly check the voltages of all my rechargable batteries before and after charging, using a simple voltmemeter. It gives an accurate reading of the voltage in the battery...and is also shows if you have got a 'dud' one.

  proudfoot 16:38 11 Oct 2011

Aichbee testing a battery off load is pointless. A battery needs to be On Load to get an idea of the voltage as there is a volt drop within the battery. On Load voltage will always be less than Off Load. The theroretical representation of a battery is a DC generator with a resistor in series beween the terminals.

  Aitchbee 17:02 11 Oct 2011

romanby1 - if I check, say 100 batteries, off load, I can very soon eliminate the 'duds'.If the actual voltage readings, off load,are below what they should be, I charge them up.Invariably, after an overnight charge, the voltage readings are higher, ie..they are 'charged up'. What could be simpler?

  onthelimit1 17:25 11 Oct 2011

I believe the old NiCads needed cycling to prevent them developing a memory. I don't think the same applies to Lithium-ion etc.

  namtas 21:50 11 Oct 2011


A battery measured off load can give a voltage that appears to suggest that it is OK but this is a meaningless test, it can still be dud in terms of output. That is why a resistance tester must be used when testing vehicle batteries.

  morddwyd 21:52 11 Oct 2011

"What could be simpler?"

Following the laws of physics, which is what romanby1 was doing, rather than your own inaccurate reasoning.

An off-load voltage test is useless.

I currently have a set of batteries which after an overnight charge will show in excess of 12v.

Put them in a mobility scooter and it won;t even go ten metres, and the voltage is down to 5 -7.

  Aitchbee 22:11 11 Oct 2011

OK - respected forum members. You have convinced me! On a similar note; can my simple ammeter/voltmeter be used to check the output current and output voltage from a charger, off load, to see if it matches the actual information on the charger?

  onthelimit1 22:49 11 Oct 2011

Not really - a battery will draw high current from the charger when flat. As it charges, the current drawn will reduce (all due to back EMF, if memory serves me right after about 50 yrs).

  TopCat® 00:34 12 Oct 2011

Here can be found some good stuff about all things battery plus a bit more. I found it very informative and useful indeed. Hope you do too. TC.

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