Dougal
Well-Known Member
Apart from a voltage reading, is there a more accurate way of testing so called 'maintenance free' flooded batteries?
Battery Testing!
- Thread starter Dougal
- Start date
savageseadog
Well-Known Member
A battery conductance test using Midtronics tester for example.
MagicalArmchair
Well-Known Member
Durite discharge tester is another option
Dougal
Well-Known Member
Errrr.... sorry, I'll rephrase that.... With whatever I might have to hand on the boat? ;-)
MagicalArmchair
Well-Known Member
Do you have a multimeter on board? 
edit: If so, you can do a drop test with that, put that on (so long as your battery is over 12.4V (viz 75% charged) else it won't be accurate) and start the engine with your starter, so long as the volt drop doesn't go below 9.6V your battery will not be paper weight material and should be okay. This is easier if your multimeter has a Min/Max function
edit: If so, you can do a drop test with that, put that on (so long as your battery is over 12.4V (viz 75% charged) else it won't be accurate) and start the engine with your starter, so long as the volt drop doesn't go below 9.6V your battery will not be paper weight material and should be okay. This is easier if your multimeter has a Min/Max function
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lw395
Well-Known Member
Test for what purpose?
You could run a known load for a long time and see how much the volts drop to establish capacity.
You could watch the voltage drop over a few weeks to establish self discharge.
You could measure its voltage when cranking if its an engine battery.
ianj99
Well-Known Member
Charge the battery overnight or by whatever means you have to charge it up as high as possible.
Disconnect the charger (& any load) and leave it 20mins. The state of charge is indicated by the open circuit voltage:
>12.75 = 100%, 12.62 = 90, 12.5 = 80%, 12.4 = 70%, 12.25 = 60%
Next connect a known load, eg nav lights etc and note how long the voltage takes to drop to about 11.8v.
Disconnect the load, wait 20mins and measure the open circuit voltage which will have gone back up a bit.
Repeat this a few times until it stays at or just below 11.96v open circuit which is approx 40% charge remaining and this is as low as you should discharge any battery for maximum life.
A good, fully charged 100ah battery therefore should have a useable capacity of 60AH - ie 6amps for 10hours, 12amps for 5hours etc, before the voltage drops below say 11.9v (30% = 11.8, 20% = 11.66
Disconnect the charger (& any load) and leave it 20mins. The state of charge is indicated by the open circuit voltage:
>12.75 = 100%, 12.62 = 90, 12.5 = 80%, 12.4 = 70%, 12.25 = 60%
Next connect a known load, eg nav lights etc and note how long the voltage takes to drop to about 11.8v.
Disconnect the load, wait 20mins and measure the open circuit voltage which will have gone back up a bit.
Repeat this a few times until it stays at or just below 11.96v open circuit which is approx 40% charge remaining and this is as low as you should discharge any battery for maximum life.
A good, fully charged 100ah battery therefore should have a useable capacity of 60AH - ie 6amps for 10hours, 12amps for 5hours etc, before the voltage drops below say 11.9v (30% = 11.8, 20% = 11.66
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Dougal
Well-Known Member
Many thanks folks. Much more to go with here now. Those silly red, green and black ' condition blobs' on them, seem about as much use as bloody chocolate tea pot!
Noahsdad
Well-Known Member
I picked up a brand new Silverline drop tester for less than £15 on line as I suspected my domestics were on their way out. Unfortunately the drop tester showed this to be the case! Three new batteries please!
William_H
Well-Known Member
Batteries "On the way out" Well in fact all batteries are on the way out. Because they have a finite life. The question you need to ask is "Is there more life left in the batteries?" Cos to throw them out early will be a waste. On the other hand if you are setting off on a long voyage and want to be sure batteries will survive for all the trip then yes change them.
On boats we have multiple batteries for redundancy when starting engine and for added capacity for services.
So it is essential that each battery is treated as an individual. Will it start the engine alone? Will it provide a deceent amount of current for a decent time. 50% of rated AH capacity would be regarded as still good.
So if a battery won't do the job you need it to do it is dud. If it will do the job reasonably then keep it. good luck olewill