With a second battery and a Hellroaring Battery Isolator/Combiner BIC-95300B installed in your vehicle, you can use energy from both batteries combined to supply the needed power for your winching application.   By doing so, you can more than double your electrical capacity!   How can that be, you may say?   To answer that question, we must understand what happens as a battery discharge rate changes. It is well known that when a battery discharges at a current that is higher than its standard 20 hour discharge rate, it will lose available capacity.  

For example:

A 50 AH battery that is being discharged at 100 Amps may only supply 18 AH (at 20C)!  

If two 50 AH batteries supply 50 amps each for a total of 100 Amps,  each of the batteries may supply 25 AH for a total of 50 AH.   This is about 2.8 times the capacity compared to using a single battery alone.   But this comparison assumes that all other factors remain the same.  The fact is, you will obtain even more capacity because the total current will be less than 100 Amps!   Because each battery will have less voltage drop internally, the terminal voltage will be higher.   The higher voltage means that there is more power available to your winch.    This also means that, for the same winching power, you will require less current.    So by using two batteries for winching, you can obtain 300 % of the capacity you would have obtained from a single battery (depending on actual load, battery size balance,  and current available from the alternator.)     As a side benefit, you will not need to discharge as deeply to get the same job done.    It is also known that the life span of a battery is inversely related to its depth of discharge.    Therefore, when your batteries discharge less deeply, they will last longer. And, with less current from each battery, there will be less stress on their own terminals. We have seen battery terminals melt off the battery during heavy winching with a single battery.

An excellent setup for this system is to connect your winch system to your main battery and wire in a second battery in a backup configuration through a Hellroaring BIC-95300B configured for high current (Backup Battery Setup).   You can choose to gain operating capacity by switching in the backup, OR you can save the backup for starting power.   Your choice!