Jack
Senior Member
Today's vehicles have a lot of accessories and features that draw a small amount of current when the engine is off. If a vehicle sits on a dealer's lot for too long, the battery runs down. Car dealers call it "lot rot".
If you have a recent vintage truck and it's parked for a few weeks, you need to deal with lot rot. It's not a problem with the camper battery if you have solar (and light) or if you remember to pull the switch and disconnect the battery.
I found out the hard way. With the stay home edict of the pandemic, we have not been able to get out of Dodge (aka Portland) since late January. A few weeks ago, I went to start the Ford Ranger and the battery was dead - 5.5V. I got it jump started and then began testing the current draw when the engine was off. I had a lot to learn. The current draw can be almost 0.5A right after opening the door. It now makes sense as the locks open, cabin lights come, and various device power up in anticipation of startup. Not realizing this, I called the Ford dealer and they had me bring it in - 500 mA was out of spec. They tested the battery and the current draw and said all was well. The maximum spec for the Ranger was 50 mA with the engine off for 10 minutes. Mine drew 36 mA after the engine was off for a while. They tested the battery and said it was good.
This still didn't sit right, so I did further testing. Because it takes several hours, I'm sure they did not do a capacity test, which is quite different than testing the starting capability of a battery. My less than year-old battery is rated for 70 Ah new, and when I tested it, it was down to about 30 Ah. Since the truck draws a bit less than 1 A/day (24 x 0.036 A), the battery will be 75% discharged in about 3 weeks.
Completely discharging the battery did the damage. Ford does not warn you about lot rot, although they do say in the manual that if the vehicle will be idle for more than 30 days to disconnect the battery ground.
The simple solution is to start the truck every few weeks and let it run for 30 minutes or so. Or, if you have 120V handy, put a decent trickle charger on the battery.
Since where I park does not have 120 V, I’ve gone with a solar trickle charger.
Big Caveat! If you get a “solar trickle charger” make sure it has a charge controller built in or you add it externally. Amazon offers many of these simple chargers and they can damage your battery. The problem is that the solar panel output ranges between 11V and 24V, depending on sunlight and solar panel characteristics. You want a trickle charge at 14.4V.
I got a 10 W panel and charger controller from amazon for about $45: https://www.amazon.com/gp/product/B082DCMFZS/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 and https://www.amazon.com/gp/product/B07QZXMWLM/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
These are not high end products, but I’m not asking much from them.
I was going to mount the charger controller under the hood, but did not find a good, easy location. And the charge controller and panel, anyway, stay home when we travel.
Another Caveat: If you install one, connect the ground wire to the truck chassis where the battery connects to the chassis. Connecting to the negative terminal of the battery can create a ground loop and mess with some of the truck's electronics.
If you have a recent vintage truck and it's parked for a few weeks, you need to deal with lot rot. It's not a problem with the camper battery if you have solar (and light) or if you remember to pull the switch and disconnect the battery.
I found out the hard way. With the stay home edict of the pandemic, we have not been able to get out of Dodge (aka Portland) since late January. A few weeks ago, I went to start the Ford Ranger and the battery was dead - 5.5V. I got it jump started and then began testing the current draw when the engine was off. I had a lot to learn. The current draw can be almost 0.5A right after opening the door. It now makes sense as the locks open, cabin lights come, and various device power up in anticipation of startup. Not realizing this, I called the Ford dealer and they had me bring it in - 500 mA was out of spec. They tested the battery and the current draw and said all was well. The maximum spec for the Ranger was 50 mA with the engine off for 10 minutes. Mine drew 36 mA after the engine was off for a while. They tested the battery and said it was good.
This still didn't sit right, so I did further testing. Because it takes several hours, I'm sure they did not do a capacity test, which is quite different than testing the starting capability of a battery. My less than year-old battery is rated for 70 Ah new, and when I tested it, it was down to about 30 Ah. Since the truck draws a bit less than 1 A/day (24 x 0.036 A), the battery will be 75% discharged in about 3 weeks.
Completely discharging the battery did the damage. Ford does not warn you about lot rot, although they do say in the manual that if the vehicle will be idle for more than 30 days to disconnect the battery ground.
The simple solution is to start the truck every few weeks and let it run for 30 minutes or so. Or, if you have 120V handy, put a decent trickle charger on the battery.
Since where I park does not have 120 V, I’ve gone with a solar trickle charger.
Big Caveat! If you get a “solar trickle charger” make sure it has a charge controller built in or you add it externally. Amazon offers many of these simple chargers and they can damage your battery. The problem is that the solar panel output ranges between 11V and 24V, depending on sunlight and solar panel characteristics. You want a trickle charge at 14.4V.
I got a 10 W panel and charger controller from amazon for about $45: https://www.amazon.com/gp/product/B082DCMFZS/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 and https://www.amazon.com/gp/product/B07QZXMWLM/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
These are not high end products, but I’m not asking much from them.
I was going to mount the charger controller under the hood, but did not find a good, easy location. And the charge controller and panel, anyway, stay home when we travel.
Another Caveat: If you install one, connect the ground wire to the truck chassis where the battery connects to the chassis. Connecting to the negative terminal of the battery can create a ground loop and mess with some of the truck's electronics.