Both Voltage Sensitive Relay and Split Charge Relay are used to manage batteries in a dual battery system, which usually consist of a main battery and an auxiliary battery.

Typically, Split Charge Relay is controlled by the ignition wire, so that when the engine is running (ignition is ON), the split charge relay will close and connect both main battery and auxiliary battery. When the engine is not running (ignition is OFF), the split charge relay will open and disconnect the batteries. While it is relatively easy to install and operate, the charging and discharging operation is hardwired so the system will operate regardless of the state and condition of the batteries.

On the other hand, Voltage Sensitive Relay senses the voltage and thus the charge level of main battery and decide based on the charge level of main battery, whether it will close and connect both batteries or not. This is a superior way of charging, make sure that the main battery is full before it will charge the less important battery (auxiliary battery). It also allow part of the main battery to be used for accessories and less important use, while maintaining the necessary charge in the main battery to crank the engine.

Dual Battery System VSR

Dual Battery System VSR

There are also some smart, integrated modules, which include not only battery management but some of the smart switching functions, which allow people to control their accessories easily with touch of a button.


Matt · 14th May 2018 at 11:30 pm

Can this system handle a 140 amp alternator?

    batteksystem · 14th May 2018 at 11:57 pm

    Yes, most of our VSR offering support 140 Amp Alternator. Our best offering support up to 180 Amp Alternator (Check our 12V 180A offering). However, we also offer 12V 50A version for ATV UTV and motobike.

    12V 140A

    12V 180A

    12V 50A

Rico · 16th October 2018 at 5:58 pm

I have read about using TWO VSRs, bi-directionally, to add another level of capacity. Guessing that Dual SENSING VSR is essentially the same ? Do you have Dual SENSING VSRs ?

    batteksystem · 1st November 2018 at 10:52 am

    Obviously using a dual sensing VSR (meaning that the relay will be turned ON whenever either one of the battery is sufficiently charged) is better than connecting two VSRs in parallel to achieve the same effect: You only have one relay and one contact resistance to deal with. There are also extra wiring and more terminals to crimp if using two VSR.

    Given the price differences of single sense VSR and dual sense VSR, I will definitely go with dual sense VSR.

simon pinnock · 6th December 2018 at 12:26 am

can you use a vsr to connect a cranking battery to an inverter and not a second aux battery?

    batteksystem · 8th January 2019 at 12:32 pm

    Yes, in this case, it should be connected to a single sense VSR. If the cranking battery has voltage lower than 12.8V, then it will cut-out and do not supply power to the inverter in order to protect the battery.

Leave a Reply

Avatar placeholder

Your email address will not be published. Required fields are marked *