Battery question.

[andyman]

Any battery experts on here. I have 2 95 amp AGM batteries. Both the same age but different makes. I always noticed that when in use, the voltage drops fairly quickly to around 12.5 volts and then stays around that level of charge.
We have 100 watts solar panel.
Just had 4 days of hook up and as always day 2, 12.5 volts and then voltage went up during the day when the sun was out . Night time back to 12.5 volts.
Got bored yesterday and was checking all the connections and then decided to see what the current draw was from Lynn's hair dryer.
On the feed to the inverter 18.5 amps, but checking each battery feed separately.
One was 6.5 a.ps the other 12 amps.
All connections are to buss bars.
Could the 2 batteries have that much difference in internal resistance, or a bad battery.

 

[Kannon Fodda]

Voltages of batteries are best checked when they have been at rest for at least 30 minutes if not an hour, i.e. no charge or discharge loads.

The voltage rising during the day is expected when your solar is using a higher voltage than the battery in order to get a input charge current to flow.

Many reasons for different current draw from the batteries. There can be different resistance from the cabling, especially if different lengths and sizing or quality of the connectors such as the crimps. But crucially the batteries are different makes which means different internals. More current will inevitably flow from the one that is a tad better at internal resistance and chemistry.

 

[Lenny HB]

For a start 18.5 amps for the hair dryer is not right even the smallest travel hair dryer on lowest setting at say 500 watts would draw about 45 amps.
The battery supplying the lower current has probably had it but your measurments sound all wrong.

 

[Jev88]

Your measured voltage Should drop when a load is applied. As said above you can only measure a battery charge at rest after 30 minutes with everything switched off.

 

[andyman]

For a start 18.5 amps for the hair dryer is not right even the smallest travel hair dryer on lowest setting at say 500 watts would draw about 45 amps.
The battery supplying the lower current has probably had it but your measurments sound all wrong.

Are you saying I can't read a multi meter. 225 watts at 240v, 18.5 amps seems about right me.
But what do I know,

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[pappajohn]

Are you saying I can't read a multi meter. 225 watts at 240v, 18.5 amps seems about right me.
But what do I know,

Yes.
225w at 240v is 0.95amps
225w at 12v is 18.75amps

And 225w for a hair drier is a waste of time. Would be quicker sitting in the sun.
700w would be far better.

 

[andyman]

Yes.
225w at 240v is 0.95amps
225w at 12v is 18.75amps

And 225w for a hair drier is a waste of time. Would be quicker sitting in the sun.
700w would be far better.

It's been fine for 12 years, 225w on low and 460 on high.

 

[Mucklestone]

Personally I think it sounds like the batteries are just getting a little old and cannot hold as much charge anymore. The fact they quickly drop to 12.5v could simply be they cannot hold any more. You could try and battery restorer but they are not always successful.

Particularly as one battery is a different make, it may be worth considering getting a new matching pair for next year....