It’s normal for an auxiliary battery’s voltage not to rise immediately even though the charger is running. Multi-stage charging delivers high current to replenish a deeply discharged battery before voltage begins to climb, which can take 30 minutes or more.
Battery chemistry, age, capacity, heat, load, and installation factors also affect charge behaviour. In general, batteries reach about 70–80% charge during Boost before moving to Absorption, and 100% at Float.
For lithium batteries, the two-stage profile means they reach around 90–95% charge in Constant Current before switching to Constant Voltage.
REDARC recommends seeking the support of a qualified auto electrician or technician.
Important
For your safety, REDARC recommends installation by a qualified technician. Seek support from a REDARC recommended dealer or installer - Find Your Local Installer
A frequent question our team receive is from customers or installers saying that although their battery charger is running, the auxiliary battery's voltage isn't rising.
This is quite normal and doesn't mean that something is wrong.
It all comes down to the way a multi-stage charging process works. When a battery is deeply discharged it will take a large amount of energy to be put back into it to make the voltage rise. This will take some time, so let it charge for 30 minutes or so and recheck the voltage.
As a more general guide, the graphs below show how the battery's state of charge (Green) will progress as the charger makes its way through the various stages of charge. Note that the horizontal (Time) axis in the charts isn't to scale.
The green "State of Charge" line is shown with a bulge to display that not all batteries will charge in quite the same way. Factors including heat, age, chemistry, capacity, loads attached, cable size/length, mounting location (amongst others) will all affect the way that the battery charges.
As a general rule, the battery will be around 70-80% charge when the charger moves from Boost to Absorption and at 100% when the charger moves to float.
The Lithium profile graph is very similar, although the charging profile is now only 2-stage. Here the battery will be at roughly 90-95% state of charge when the charger moves from Constant Current to Constant Voltage stage.
