Testing batteries.

[nicho]

We have 2 x 120 amp/hr batteries linked for domestic supply on our Bavaria 34 and I would like to test them. Do I have to disconnect the two from each other and test individually, or is it possible to check individual batteries with a tester while still connected. Forgive my total lack of knowledge with all things electrical! Thanks

 

[pvb]

Disconnect them and test individually. It's not easy to test domestic batteries. One thing you could do is connect a known load and see how long it takes for the battery to drop to 12.1v (about 50% discharged). A 60W car headlamp bulb will draw about 5A. You should then be able to calculate a rough capacity for discharging down to 50% (and you really shouldn't let batteries go lower).

 

[nicho]

Disconnect them and test individually. It's not easy to test domestic batteries. One thing you could do is connect a known load and see how long it takes for the battery to drop to 12.1v (about 50% discharged). A 60W car headlamp bulb will draw about 5A. You should then be able to calculate a rough capacity for discharging down to 50% (and you really shouldn't let batteries go lower).

Thanks, I have purchased a battery tester which applies a load for 10 seconds and reads and displays the battery condition. Tested it on the car battery, so I know how to use it (the battery didn’t seem to come to any harm!). The boat batteries are connected to a smart charger which keeps them topped up, but I am trying to ascertain if they are good or on their way out.

 

[pvb]

Thanks, I have purchased a battery tester which applies a load for 10 seconds and reads and displays the battery condition. Tested it on the car battery, so I know how to use it (the battery didn’t seem to come to any harm!). The boat batteries are connected to a smart charger which keeps them topped up, but I am trying to ascertain if they are good or on their way out.

Those testers can be imprecise. They're OK for starter batteries, but won't necessarily tell you much about domestic batteries.

 

[nicho]

Those testers can be imprecise. They're OK for starter batteries, but won't necessarily tell you much about domestic batteries.

OK, understood, thanks pvb

 

[starfire]

Put it in perspective, my battery tester cost over £300. You get a nice printout though

 

[nicho]

That’s a massive perspective.........I bought a Silverline one off Amazon for £18?

 

[vyv_cox]

I believe that leisure type batteries can be damaged by drop-testing. The headlamp bulb method suggested by pvb would be safer.