Battery Recharging While Driving

Question: We travel south in the winter with our fifth wheel and on the way down stay in Walmart parking lots. The first night we turn on the furnace and all is well. The second night the battery hasn’t charged up enough to run the furnace.

We drive more than 8 hours per day so I was thinking the battery should be charged up enough to run the furnace the second night as well. This year I replaced the old battery with a larger marine deep-cell style battery hoping this will help the situation. Any help or ideas would be appreciated. Would getting the best RV battery help?

How to Charge Battery While Driving

Answer: When we first answered this question, we suggested that you might have a problem with your charging system – especially since it sounded like you had been successful in the past in charging your 5th wheel battery via the truck.

However, we received a comment from one of our readers that made us rethink our previous reply. The reader questioned how the truck was charging the fifth wheel. So let’s start with that consideration – how the trunk/vehicle electrical system would react to the new larger battery.

Many trucks/vehicles pulling a trailer will provide a charge to the trailer battery while driving down the road. However, that charge will not be enough to sufficiently charge a depleted battery. The reason for this is that the truck will initially provide a high charging rate but will taper off as the truck’s own battery reaches its full charge – which will be much sooner than the trailer battery requires. So that leaves you with a partially charged trailer battery.

Since the truck charging system is only wired to regulate itself, it does not sense that the trailer battery still needs a substantial boost.

There are steps you can take to help alleviate this problem, but it will require an investment in time and money. Some simple steps would be to substitute the 12-gauge wire that provides the charge with a eight-gauge, or even better six-gauge, charging wire (the heavier the gauge the less flexible it becomes).

Another “fix” would be to get a battery-to-battery charging system. We have read about a Sterling battery-to-battery charger but we have no experience nor are we familiar with the product. We just mention it in case you want to go and look at an alternative solution. You can check out the Sterling website.

Having said all the above, perhaps you have already configured things so that your truck adequately charges your 5th wheel battery. If so, then there is a chance that there is some sort of problem with the charging system. Perhaps the new battery is not being adequately charged by the charging system of the truck. It might be worth it to check out the battery and charging system (alternator, voltage regulator, charging solenoid, etc.).

Another consideration is that the new larger battery may be putting too much of a strain on the charging system and will require longer charging times than what you are used to. Is it possible that you are running any appliances while driving, which might cause an additional draw? Or perhaps the new battery is defective and is just not holding a charge. The battery manufacturer may be able to shed some light on this by providing an estimated charge time based on charging rate.

Other thoughts welcome. Please let us know the outcome.