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How to Charge Truck Bed Camper Battery from Vehicle

Question:

You say that 12 V supply coming through a seven pin connector is sufficient to top off a camper battery but not enough to charge a dead battery. On our maiden voyage in our new lance 650 camper the battery went dead in four days. We did quite a bit of driving every day - not cross country but exploring the area. I never had that problem with my Perris Valley on a Chevy S10. Much like the truck battery The camper battery was topped off in 20 minutes to an hour. The dealer is telling me this is just the way it is but it can’t be because it’s ridiculous to have a battery that doesn’t charge. What are we supposed to do stop and borrow somebody’s plug for a day just to charge the battery? Anyway if it’s a question I’m posing it’s why isn’t the battery being topped off? Could an over-long run of the 12 V circuit be the problem? The camper plug comes out of the front of the camper but the truck plug is in the back of the bed so our has to come the entire length of the truck plus the length of the bed and then whatever route it takes with the camper to get to the battery.

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Expert Reply:

You are on the right track to answering your question of "why isn't the battery," being charged as the reason is that the charge circuit of your vehicle just can't carry enough amperage/voltage to keep the battery charged. The reason this is the case for your new setup is most likely because your new camper has a larger battery and/or has appliances that just draw more which uses more of the battery and the current circuit just can't keep up. So the wiring of the 12 volt charge circuit of your vehicle is going to be to thin and ran for too long of a distance to provide an adequate charge.

So the solution is to run a new charge circuit from your vehicle batter/alternator that can deliver enough amperage/voltage to keep the camper battery charged. To do this the new wiring will have to be MUCH heavier than what you currently have. So I recommend 3 gauge winch wiring witch quick disconnects. For that you'd want the part # BDW20025 for a 7-1/2 foot section that will wire to camper battery and then for the section that installs vehicle you'd want the 16 foot long section part # BDW20043. The quick disconnects allow you to easily disconnect the wiring if/when you remove the camper from your truck bed.

Now if you wanted a way to prevent the camper battery from accidentally draining the vehicle battery when it's not running you'd need to install an isolator. For that you'd need the part # 331-SBI12 and you'd be set.

expert reply by:
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Jameson C

Question:

Thank you for your thorough explanation. I just took the camper in yesterday to the dealer and they did electrical checks on the system and said everything was “up to spec.” They measured 13.4 V coming from the truck at the battery (although I thought I read somewhere that 14.4 was necessary to charge.) One of the things they brought up was that this new lance camper has a lot more gizmos drawing current even when everything is off such as 2 carbon monoxide monitors, smoke alarm, radio, tv, etc. So the bottom line is that you believe the truck’s alternator is capable of keeping the camper battery charged if it’s got sufficient current carrying capacity in the connecting wire. Correct? The reason I ask is I don’t want to spend all the money and take all the time and energy to do the wire upgrade only to find out that there’s just not enough output from the alternator to keep the camper battery charged.

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Expert Reply:

Your alternator would have enough amperage to also charge the second battery as long as the circuit that connects the alternator to the battery has a heavy enough gauge wire like what I mentioned. If you look at the wire that connects the alternator to the vehicle battery you'll see that it's also very thick. Alternators rarely use their full capacity and most of the time the voltage regulator is pulling back the amount of amperage it charges since more power is produced that can be used.

expert reply by:
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Jameson C

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