13 Volt battery?

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richardabeattie

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I have a 2 year old Varta 12 volt 61 AH battery for engine starting. It was well down so I took it home and gave it a long reconditioning charge using a CTEC smart charger. That brought the voltage up again to over 13 volts. 24 hours later without having reconnected it to a load the voltage has dropped a bit but it is still at 13. Is this normal?
 
A fully charged battery will read a little under 13 volts (more like 12.6 volt). Without any load on it, it will stay above 12 volt for several days. Weeks maybe.

Put some charge on it and it will soon drop to 12 volt and carry on downwards.
 
I have a Varta Leisure battery.

It is several weeks since last on charge. It currently reads 12.84 volts.
 
richardabeattie said:
Could you expand on that a bit? How long does it take to drop to its normal working level?
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The charged voltage of a battery when new starts around 12.8, over time this increases to above 13 volt, then slowly back to 12.7 / 12.8, time scale depends on usage but can be over an extended period.

One of the problems trying to ascertain battery capacity, nothing is static.

Brian
 
Your replies fill me with gloom. The battery is clearly OK. The Alternator is alternating. So something is draining the battery when all systems are ostensibly off. I'd rather have bought a new battery than a new loom!
 
richardabeattie said:
Your replies fill me with gloom. The battery is clearly OK. The Alternator is alternating. So something is draining the battery when all systems are ostensibly off. I'd rather have bought a new battery than a new loom!
Click to expand...

Okay, put the battery back on the boat, connect it up and turn on the cabin lights so you are drawing a few amps, then monitor the voltage, is it falls slowly over a few hours battery okay, if the voltage falls rapidly over 30 minutes it's the battery.


Brian
 
Was it over the winter period that the battery was left to it own deviced and fell from 13 volts to 12 volts between October and May? Do you have anything permenetly connected when you are not onboard such as a battery monitor or gas alarm?
There could be some leakage current of a few milliamps which over 6 months will drain the battery.
 
You can't really test a battery with a voltmeter. You need a battery drop tester. They are not something you would ever buy, but any auto parts store or garage will have one. Insist that they let you watch them do the test!
 
CreakyDecks said:
You can't really test a battery with a voltmeter. You need a battery drop tester.
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This is very bad advice if you are talking about service batteries!

A drop tester is designed to test starter batteries under a high load not deep cycle service batteries under low loads. A starter battery uses about 1% of its capacity each time it is used! A service battery could use 50% each time it is used. A drop tester will tell when a battery is dead but not how much life it has left in it. A deep cycle battery may easily pass the test to deliver a high current for a short time, but if their capacity has been reduced by sufation then these testers cannot test the remaining Ah capacity so the batteries life at anchor may be very limited.

You can test a battery with a voltmeter, but you must use a small load and see how quickly the voltage falls.
 
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There are more advanced versions of the drop tester which require you to set the details of the type and capacity of battery and it calculated the CCA available (high load) and must then spend the next few minutes on low load, before it produces a calculation of the remaining capacity. These two are to some extent dependent on the charge state, of course, and the tester also gives the charge state based on the resting voltage and concludes whether the battery is in any way serviceable. We tested two on my boat a few years back. One had little capacity left and has since been thrown as it was of little use even as a 12v bench supply at home - any load noticeably dropped the voltage. The other nearly achieved its design CCA and capacity despite being "dangerously" low in charge - bourne out by the fact that it is still (5 yrs later) being used in my caravan, happily doing a week on a single charge. I'd have left it on the boat, but it's always suggested that the pair should be replaced together.

Rob.
 
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