Things To Know When Charging Trailer Battery From Vehicle 7-Way Trailer Connection

Question:

Hi, according of this answer: question-24390 for exemple my battery is flat on the trailer , as soon as I plug the 7way plug of the truck. Do Im gonna blow fuses on the truck if the auxiliary battery is completely discharged in the trailer ? If im not powering any accessories in the trailer.. Does it creates a draw effect ? Both battery will equilibrate themself? How many amps will be delivered in the 7 plug for my trailer battery? the truck is not running, and I have 12V output still in the 7 way plug

asked by: Patrick T

Expert Reply:

Your trailer battery can be charged by the 7-Way 12V blade. This is a maintenance charge only, so if you have a dead battery, you would still need to connect it to a standard battery charger like the NOCO Genius # NOC34FR to get a decent base charge. The amperage delivered to your trailer will vary based on your vehicle alternator. Most alternators will run about 14 amps so what is not required to charge your vehicle battery will be sent to your trailer battery.

If you run a direct line from your vehicle battery with a 40 amp circuit breaker like # 9510 and # 10-1-1 wire, that is the norm and will provide only that maintenance charge due to amperage and distance from the alternator to your trailer battery. You will not blow fuses if the trailer battery is completely discharged, but you most likely won't be able to charge it from a completely discharged state either. Without this, anytime the trailer is connected it will have a power draw. The batteries will eventually equilibrate themselves as you stated and that can be a bad thing.

If you want to make sure that your vehicle battery only charges the trailer battery when the vehicle is running, you can add a solenoid like # PK5231201 which will have the accessory in the middle to attach to your ignition. This will ensure your vehicle battery is not drained by your trailer battery and you'll be able to have the cranking amps needed in your vehicle battery to not leave you stranded.

expert reply by: Jason S