Battery Charging

[johnboy007]

hi. Folks, can anyone help. Following heaps of advice about car Battery charging I have been told that my car Battery sitting at 12.3 -12.4 volts would be approximately 50% charged and with a 4 amp charger would take only 3-4 hours to fully charge. I have now done this and went to work yesterday with the comfort that the Battery was 100%, and when I got home in the evening checked with a meter and found the Battery was at 13.0 volts, so I was ecstatic. This morning I re-checked the voltage and found it was at 12.4, back to 50%, so am now confused. Have read up a lot about charging and the census of opinion is that the reserve capacity of which mine is 135, should be multiplied by .6 to give the amount of amp hours needed to charge (81) divided by 50 as 50% is missing, which gives 40.5, and thereafter a charge rate of 4 amps ( which my charger puts out) calculates to 10 hours of charging @ 4 amps (40.5/4). Should I therefore go & charge my Battery which has 12.4 v for a further 10 hours to fully charge it?.

The fact it read 13.0 after a 20 mile trip down to 12.4 12 hours later is confusing me, is the charge from the alternator a false indication of a batteries charge ?, or do I maybe have a drain somewhere... Thanks for listening , John

[ROYT]

If the Battery was on the car, any alarm fitted, clock etc will be slowly draining it down overnight or when parked etc.

If after the charging you gave it it cranked the engine lively and everything works OK then it's charged OK

If it is failing it will be very reluctant to crank a cold engine.

Confirm the alternator is charging by putting a voltmeter across the battery[engine idling] and

have someone increase the engine revs. to say 1500, the voltmeter should show approx 12.5-14.5 volts.

Repeat this with headlights and heated rear window on, should still be more than 12 volts.

If not alternator fault.

Remember if you only do short journeys with wipers, heater etc on, the alternator will struggle to replace

what you are using, and the Battery may need a 'top up' from your charger

After this if the Battery will not hold charge, time for a new one!

[Or as you say a drain somewhere, boot light stuck on or something..]