odd voltage graph from my bowtruster battery ?

[simonfraser]

took boat out at 10am, OB off 12:30

hauled anchor up 4x in short succession with the motor running, managed to hook a tyre and then some weed

later in the day plugged my phone in to charge, which is off the same battery, both in the forepeak

as i plugged the phone in the voltage dropped ?? blue top AGM battery, 3 yrs old

i ran the motor the next day an hour before lifting the anchor no prob

should i be concerned about he graph below:

 

[[2574]]

Simon,

That's very interesting, I have the same battery type deployed as the bow thruster battery, and it too rests at about 12.6v. Battery is two years old and has been off charge and isolated since the end of September when we put the boat ashore. Here are some graphs:

1) Battery temperature - the past 48hrs in Scotland has been cold and battery temp has dropped which has implications for resting V:



Currently at 4deg C as you can see.

2) Battery resting voltage:

You can see below that since last charge about 20th September, the voltage has been fairly stable, for the last month it has been at 12.6v. In the past 24hrs it has dropped a little due to the ambient temperature.



3) Ambient conditions

I'm thinking that the very gradual fall in resting voltage over weeks is also probably due to the reducing temperature trend:



I was concerned about the battery resting at 12.6v so contacted the supplier. I had a response from the battery manufacturer which in essence said that this is a normal observation and should not be cause for concern. The battery has performed without any observable problem issues whilst in use so I've accepted it as the norm, whether that be so remains to be seen in battery longevity I guess.