Tow car battery power drain

[Mercer]

We have a 2007 Honda Odyssey for a tow car. The tow car battery is trickle charged from the RV when being towed. However, the battery is drained on the second or third day of towing even though we start the car each morning. Do Honda's have unusual battery drain, or is it our car.
Has anyone had experience using a Solar Battery charger while towing the car.

[tom wilson]

my guess is the toad battery is not being charged when hookedup. get the multimeter hooked to the charge wire when the motorhome motor is running and see if the volts are 14 or more? the charge wire should show more volts than the toad volts.

[GaryKD]

Hi Mercer,
Welcome to iRV2. If your current setup is not performing or inadequate consider this product. I've been using this for about two years. I've had no problems and it works as advertised. I would make the same purchase again.

[Gary RVRoamer]

Many newer vehicles suck a lot of amps with the key on. Too many electronic systems are active, checking for remote doorlock signals, reading system status all over the vehicle, waiting for somebody to push one of the myriad of buttons on a modern car. My GMC Acadia pulls more than 10A at all times while under tow unless I remove a major fuse.

Since Honday does not officially approve towing their post-2006 vehicles (except the CRV), you probably can't get any guidance from the owner manual or a dealer, but maybe another Odyssey owner has figured that one out. Or check an 05 or early 06 Odyssey manual to see if it says anything about pulling a fuse or disconnecting the battery.

The product GaryKD suggests is a good one and will probably be enough to get you by (10A). It wasn't enough for my Acadia, though.

[Mercer]

When a battery pulls 10A is that Amps. Sounds like a lot of power being pulled from a battery. If a car battery is 12 volts, how low in voltage can it go before it will not start the car engine. Also, at 10 Amps how long will it take to draw down a battery to the point that the battery will not start the engine.

[Gary RVRoamer]

10A = 10 Amps.

It varies with the size of the engine and thus the power needed to start it, but a battery will cease to start a car somewhere around 11.5-11.8 volts. 12.0 volts is about 50% charged (a fully charged 12v battery is actually 12.6 volts).

A fully charged car starting battery can probably deliver 10 amps for around 4 hours when new, but the time drops as it ages. That's just a guess, though.

[Field Trip]

We tow our 05 Jeep Grand Cherokee Ltd and our 07 Mini Cooper, both 4 down.

After a trip of a couple of hours, both batteries will be drained from having the ignition in the acc position.

The Jeep needed a new battery, as it was 4 years old, but the Mini only has 13k miles and it's battery is in good shape.

I've debated on installing a battery disconnect in both of them, but have concerns regarding the on-board computers and their memory functions, particularly the Mini.

Another consideration is to wire a battery tender directly to the batteries and use the inverter from the coach to power the 110 for this piece. This would be easy on the Jeep, but a real pain in the Mini as the battery is in the trunk (hence the term Mini).

The toad charge is also an option.

Any suggestions as to how to best resolve this?

[Brian_R1]

I don't have a lot of experience with RV's, but with a longtime sailboat background, I do know quite a bit about batteries. Any kind of sustained load, whether its 4A or 10A, if not accompanied by a constant charge (normally supplied by the alternator) is going to kill (permanently, not just as in needs recharging) a regular car battery in short order, as you are now using it in a "deep cycle" type duty. A normal car battery is not designed for that type of duty and will experience drastically reduced life.

It seems to me just "running a wire" between the coach and toad batteries is a bad/dangerous idea because if the toad battery DID become deeply discharged there could be large (100's) of amps attempting to go through that wire, unless that wire's HUGE, like "000 AWG" or better, something's going to smoke. At the very least, if you do just run a wire, check a 12V current load table and install an inline fuse rated for whatever wire gauge is used.

A product such as mentioned above to keep the toad charged seems like a sound concept as it serves to return the toad battery use to the design parameters, ie charge in=load out with no discharge/recharge cycles. It also appears to limit the charging current. 10A is probably adequate for most (especially older) cars, but as also mentioned, newer cars are adding more and more parasitic loads, apparently 10A is no longer enough for some.

[Pusherman]

GaryKD's post above has the product to solve the toad charging issue safely. Here is the link Gary provided.

[Gary RVRoamer]

I'm surprised to hear the 05 Grand Cherokee suffers from battery drain - most Jeeps of that vintage don't have that problem. Have to wonder if there is not some other problem there.

I'd use the Toad Charge or a simple 10 ga wire with a 10-20 amp auto reset circuit breaker from the coach batteries to the toad. That should be fairly easy to set up in both vehicles. If you feed the charge circuit from an ignition switched source on the coach, you don't have to worry about running down the coach chassis battery(s) while stopped. Or use the house batteries as the source - they can get charged later (or will be charged as you drive on some coaches).

[Gary RVRoamer]

Field Trip...
Check your owner manual for the Recreational Towing procedure - I think you may have the key in the wrong position (ACC) and that is causing your battery drain problem. According to the 2005 GC manual that I read, the key should be in the "unlocked Off" position" for towing. Your GC has the Sentry Key system (chip in the key), so the steering wheel is not locked when the key if Off. That allows towing in the Off position.

Please verify this in your owner manual, but I think that will solve your battery problem.

[Field Trip]

Gary,

We're the original owners of this GC, and not once did I ever verify the fact that it does not have a steering wheel lock.

The GC's problem is solved, now on to the Mini Cooper... It does have a steering wheel lock.

The dealer advised against a battery disconnect as the computer maintains a memory (short answer for a 30 minute conversation).

Thanks all for your input!!!