Thread: Wiring up a winch with 2 batterys

I have just installed a 2nd battery only for winching last week. I had the same question and asked my local auto electrician. He said the problem with linking the 2 batteries directly together is that you will never get them both to fully charge. The weaker battery will always drag the better battery down to it's level.

I have installed a 100A solenoid between the 2 batteries (this is not the sensing type as ARB sell but just a direct switching solenoid and cost only about $20). I have wired the solenoid to a switch on the dash along with another volt meter for the 2nd battery. I can then link the 2 batteries while I am driving for half an hour so it gets charged up then seperate them until I need to link them when winching. This ensures the main battery always gets fully charged.

Then again you could install a dual battery system but I wanted to do it cheaply.

Purely a personal opinion, but I would not do that. If you flatten the battery with your winch then you are stranded. I know as a general rule it is recommended that you connect the winch to the main battery even if you do run an auxiliary.

Common sense tells me in your situation I would have the two batteries connected by a heavy duty battery switch and connect the winch to the auxiliary battery. Then you could isolate it if you were at risk of draining both batteries and at least have some kick left to start the engine if needed.

That way you have the options rather than having a fixed connection.

I have mine and radio equipment connected to the auxiliary battery. If the battery goes flat and I still need to do some winching I can simply disconnect the winch lead from the auxiliary and connect it to the main battery. Thing is, it is my choice when or whether to do that.

I am sure others will have further opinions to consider.

Hi Piddler, the most common set ups I have come across is with the winch wired up to the main cranking battery and to have the motor running when ever the winch is in use. This way, not only do you have more power for winching, the battery will last longer and even if you do pull the battery down to a level that would normally not start the vehicle, the motor is already running so you just leave it running to get the battery charged up a to a safer level.

Hi Walker, once your motor is running, there is no way the alternator can tell if one battery is at a lower charge voltage than another or if one battery is only charging to a certain level while the other is charging to a higher level.

In very basic terms, all the alternator does is to try and produce enough current, to counter any draw on the electrical system, in an attempt to keep the vehicles voltage level at that set by the regulator.

The alternator has no idea whether a current draw is coming from either or both batteries, from your driving light or air conditioner, your stereo system and so.

With your set up, once the motor is running, just leave both batteries connected to the charging system and both will eventually be fully charged.

Cheers