How to tell if batteries need replacing

[ColinR]

How to tell if batteries need replacing
They haven't failed, but are 7 years old. I have two Trojan 130 AH lead acid batteries for the house supply with a decent charging set-up, digital regulator and solar panel. All the cells look fine with a hydrometer test but when I've got normal cruising load they fairly quickly drop to 12.4v and stay around that voltage for quite a while. This is lower than in previous seasons. As they haven't failed I'm not sure whether to keep going with them or if it's time to replace them. I usually spend a couple of months a year on board and don't frequent marinas that much so often need to be self sufficient. Any thoughts welcome! Colin

 

[Catalina36]

Dunno, but age is not necessarily an indicator. My two 180ah domestic batteries and the engine start battery were on the boat and of indeterminate age when I bought it in 2005, 15 years ago. Since then I've added a dedicated windlass/thruster battery 13 years ago which I still tend to regard as "the new one" and two more in parallel 4 years ago to give me 24 volts for modified 24 volt bow and stern thrusters.

They're all still alive and kicking. Now I've said that they won't be...

 

[KompetentKrew]

Plymouth Battery Centre have a machine with which they very helpfully tested my batteries last autumn. If you're not near there, maybe your local place has the same tester?

 

[LadyInBed]

I would separate the bank, run off one of them until the voltage drops to 12.4 then swap them over and run off the other until the voltage drops to 12.4 with the same load, then compare the usage times and SG's at 12.4 to see if there is any significant difference.

 

[peteK]

A quick test that I do but not conclusive is to fully charge the battery and leave it with out any load for a few days it should stay above 12.6V

 

[PaulRainbow]

A quick test that I do but not conclusive is to fully charge the battery and leave it with out any load for a few days it should stay above 12.6V

I did this on two boats last week, left the batteries disconnected for 4 days, checked the voltage each day, no noticeable drop in voltage.

Reconnected them and applied some loads. 2 hours later one boat was down to 9v, the other was down to just 6v.

 

[William_H]

Essentailly you continue to use the batteries until the loss of performance gets to be a problem. Either the engine start is too sluggish when using the house battery. (test occasionally as this is your back up) or more likely you find the voltage drops too quickly and needs a charge more often. Discharge below say 11.5 volts is bad for them but then that may be because they are too old anyway. ol'will

 

[MikeCC]

If you get the batteries tested somewhere, make sure it's a load test that takes a few hours as shown above. A lot of the instant testers won't tell you the capacity of the battery.
If you do it in situ to give yourself an idea, it's useful to know what current you're drawing.

 

[Porthandbuoy]

Looking at the chart, does the 165Ah/20h mean a current of @ 8 Amps, or @ 100W, for the test?

 

[pcatterall]

Now and again we do a test by putting on a fairly high load, all lights instruments fridge etc and with no charge ( shore power and solar off) we record volts every hour down to 11.8 volts. If we have had as many amp hours as expected then we are happy. especially as the 11.8 bounces back a bit when load removed.

 

[Graham376]

Seven years is a reasonable time for Trojans if they have been under charged with solar not giving out the 14.8volts bulk/absorption needed, that's what I suspect killed our previous set before uprating panels. The rate price increases are running at, maybe best to replace soon.

 

[KompetentKrew]

Looking at the chart, does the 165Ah/20h mean a current of @ 8 Amps, or @ 100W, for the test?

I'm not sure what test load was used, but 165Ah/20h is the specification of my batteries.

They're the same model as this:

I would guess the dotted lines in the chart indicate the range of performance, between acceptable and brand new, as the black line is clearly the actual performance. I have another chart for the other battery in which that line stops after 4 hours, as they took it off charge having decided it too was perfectly fine - it followed the exact same trajectory.

 

[Beneteau381]

I did this on two boats last week, left the batteries disconnected for 4 days, checked the voltage each day, no noticeable drop in voltage.

Reconnected them and applied some loads. 2 hours later one boat was down to 9v, the other was down to just 6v.

I did the same when we were in Gib, nine years old and seemed healthy but a 25watt bulb on a "fully charged" one soon showed up its frailty! A couple of days later it got seroously hot and stinky! We were lucky! It was on a real melt down!