I have recently bought 2 new pump controllers with the express intention of saving my batteries! ( I would,at this stage prefer not to mention who i got them from)
I also at the same time bought 2 new batteries. I have a volt tester and when the "battery low" light started flashing I checked how low the voltage was,this turned out to be 11.5 v. The battery that I started to use had a reading of 12.6 v but wont run (battery light flashing!!) I fully charged the new battery, this took about 2 to 3 days to fully charge and repeated the process with the same results. By the way, i had to revert to bypassing the controller to carry on working with the older battery.
I have now checked this a few times to make absolutely sure that i am not imagining things and have also bought another volt checker to "prove" my findings and this confirms things. I am very confused that the fully charged older batteries wont run through the controller and yet the newer ones do, even when,when checked are at a lower voltage!!
Any technical thoughts from anyone?
You're right; on the surface this doesn't make sense.
Manufacturers of 12 v electronic equipment seem to all agree that if a battery drops below 10.4 volts
under load then the battery will be damaged. So both Spring and Varistream controllers have set this as the low voltage cut off point where the electronic controller switches off. Webasto diesel heaters employ the same cut off point.
A faulty battery could well drop to this voltage under load, and once the load is switched off, that battery voltage will 'jump' back very quickly to show a respectable voltage. So you really need to take a continous voltage reading from when before the battery is put under load, put under load conditions and the result and watch exactly what happens.
A drop in voltage could mean that the battery has a faulty cell, or one that is more faulty than the others. It could also indicate that the battery has very little capacity left due to age and sulphation. My gut feeling is a faulty cell as this minics a battery failure my daughter in law suffered at the start of this winter with her car's battery. But it may still be able to push enough power out to run the pump but once connected to the controller, the controller stops the supply to prevent battery damage.
Simon Trapani is right, Spring do have a voltage over ride on their controllers whereas Varistream do not/or didn't. Using this facility on a Spring Controller will be a temporary measure. A new battery is able to supply the voltage under load so everything will work as normal.
I would be pretty certain that even after charging your old battery for 3 days, a load tester at a battery supplier/motor factor/motor workshop will flash it up as faulty within a few moments.
