Check Your Battery

Mon Apr 06 2020

If like us you're sheltering in place, you probably aren't driving as much as usual - but don't forget to check your vehicle's battery!

Check Your Battery


We've got a lot of articles on this website about batteries - but usually we're talking about the batteries in our RV! Well, not today. Today we're talking about the battery in your tow vehicle - for us, that's our F-150.

At the moment, we're staying in one place for 14 days at a time before we have to move, which means our truck is sitting, unused, for 14 days at a time too. Although we're not running anything in the truck, the battery will slowly discharge over time. Normally, the alternator would recharge the battery while you're driving, but we're not driving anywhere!

A good, healthy battery will happily last many weeks (or months) of just sitting there. But our truck is 4 years old and still has the original battery so we need to keep an eye on it.

How has COVID-19 changed our plans?

The world seems a very different place compared to just 2 weeks ago - things have changed, and so must we.

How has COVID-19 changed our plans?

Out of curiosity, last week I went out and checked the battery on our truck. It was low. Low enough that when we moved a couple of days later, the truck alerted us to a low battery condition. Fortunately it wasn't so low that the truck wouldn't start, but had we left it much longer it could have been.

So today we're going to look at how to check your battery, what to do if it's too low, and how to stop it discharging in the first place!

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Checking Your Battery

The battery in your vehicle is almost certainly a lead acid battery - and in most cases, it's a Flooded Lead Acid (FLA) battery. That makes it relatively easy to check the condition of your battery by checking its voltage - just make sure that the battery has been resting for at least an hour or so before you check it.

There are two ways to check your vehicle battery voltage. The first, my preferred way, is to use a digital multimeter that can measure voltage.

Digital Multimeter

I have a Uni-T UT210E digital multimeter that I love because it also has an "amp clamp" to read DC current in a wire. I keep it in my truck center console at all times so it's always on hand if I need it. You can also find simpler (and cheaper) ones such as this AstroAI Digital Multimeter that can still measure voltage and a lot more too!

To check the battery voltage with a digitial multimeter:

  1. Pop the hood on your vehicle (with the engine off);
  2. Move aside any rubber coverings on the battery terminals;
  3. Switch your digital multimeter to its DC Voltage measuring setting, and if it doesn't have an auto range mode, set it to the lowest value above 12V;
  4. Touch the black probe to the negative (black terminal) on your battery and the red probe to the positive (red tereminal) on your battery.

If you get the probes backwards it doesn't matter - your battery will just show a negative voltage.

Uni-T UT210E Non-Contact Digital Multimeter
Measuring the voltage with a digital multimeter is the most accurate method.

As you can see, our voltage was 11.79V - more on that later!

Cigarette Lighter Volt Meter

While I'd recommend a basic digital multimeter as an accessory any RVer should have for simple fault finding, there is an even easier way to measure your vehicle's battery voltage.

You can use a cigarette lighter volt meter. This simply plugs into one of the 12V cigarette lighter outlets inside your vehicle and reads the voltage on a little display.

Make sure you plug it into a 12V outlet that has power even when the engine is off because if you turn the engine on, you won't get an accurate reading. Once the engine is on, the alternator will start charging the battery and you'll see a much higher voltage than your battery is really at.

Comparing Voltage

Now you know what your voltage is, but what does that mean? How charged is your battery?

Simply compare your battery voltage to this table below to check. Remember, this is only accurate if you've left your battery resting for at least an hour beforehand.

VoltageCharge %

If your battery is at 12.06V or lower, it is below 50% which can be damaging to lead acid batteries. You want to charge it as soon as possible!

Charging a Low Battery

As you saw in our photo earlier, our battery was at 11.79V. Comparing that to the chart above, that means our battery was just over 30% - that's really low! I've double checked that nothing is plugged in inside the truck that would be creating a phantom draw, so I suspect our battery is nearing the end of its life.

How can we charge it up?

The quickest and easiest way is to turn the engine on - if you can! Once the engine is running, the alternator will begin charging the battery. You'll want to leave the engine running for at least a couple hours to make sure the battery is fully charged.

But what if your engine won't start?

Dead Battery in the Desert
We're out in the middle of the desert on our own - not somewhere you want to be stranded with a dead battery!

Well, first off, don't panic. But the vehicle will need a little bit of assistance in getting started.

Why we love our Ford F-150

It's hard to find a vehicle that's a comfortable daily driver, performs well off-road and is able to safely (and legally) tow our trailer. Our Ford F-150 manages it all and we love it!

Why we love our Ford F-150

Portable Jump Starter

Since we hit the road, we've been carrying around a portable jump starter. They don't sell the exact one we have any more, but it's very similar to this one by DBPower. It's inexpensive and relatively small, but it packs a punch - even able to start some large diesel enginess.

It's important to keep it charged up, but I check it from time to time and plug it in if necessary. Fortunately, since it has a lithium battery inside, it doesn't lose much charge over time.

Portable Jump Starter
Connecting up a portable jump starter is just so much easier than jumper cables, plus no extra vehicle required!

We've used ours a couple of times since we had it to help out other motorists - it really does work, and it's so easy to use! Check the instructions that come with yours, but for ours we just connect it to the battery terminals (red to red, black to black) and turn it on.

I've had best success by waiting for a few minutes before trying to start the engine. Once the engine is running, keep it running for as long as possible - at least a couple hours - to let the alternator charge the battery.

Jumper Cables

If you don't have a portable jump starter (and if you don't, buy one now before you need it), the other option for self-rescue is jumper cables.

We carry around a pair of high-current 6ga jumper cables rated to 500Amps. This means they can jump relatively large engines, but if you have a big diesel and want to have even bigger cables, check out these Energizer 800A 1ga jumper cables!

Honestly, if I were buying jumper cables again now, I'd go with those because there's really no downside in having larger, heavier cables other than cost. And when you're in that emergency situation, that extra cost seems very worthwhile!

Using jumper cables is straightforward, but the order of connecting things is very important:

  1. Park a vehicle with a good battery close enough to the one with the dead battery that the jumper cables will reach between the engines on the two vehicles;
  2. Pop both hoods and move aside any protective covers on the batteries;
  3. Connect the positive (red) clamp on one end of the jumper cables to the positive terminal on the dead battery (usually red);
  4. Connect the other positive (red) clamp to the positive terminal (usually red) on the good battery;
  5. Connect one of the negative (black) clamps to the negative terminal (usually black) on the good battery;
  6. Connect the other negative (black) clamp to a piece of bare metal on the frame of the vehicle with the dead battery - away from the battery itself or any fuel hoses. This may spark when connected and you don't want those sparks near the battery or fuel hoses;
  7. Start the engine on the working vehicle and let it idle for a few minutes;
  8. Start the engine on the dead vehicle (hopefully!) and let it idle for a few minutes;
  9. Remove the clamps in the opposite order you put them on: dead vehicle negative, good vehicle negative, good vehicle positive, dead vehicle positive.

Obviously you need to take care when doing this that the jumper cable clamps don't touch one another or sparks will, quite literally, fly!

I have used the jumper cables a few times - once to jump start my old ATV! But since we picked up the portable jump starter, I've only my cables once - the portable pack is just so much quicker and easier to use, and doesn't involve moving my truck.

If you end up in a situation where your portable jump starter isn't charged, or just can't provide enough juice for a really dead battery on a big vehicle (like the big diesel truck with a very dead battery in winter that we helped out), it's good to know you have the jumper cables with you!

Whichever way you use, if a battery has died once it's a good indication it may be starting to fail - keep a close eye on it and be prepared to replace the battery if it keeps happening.

Keeping Your Battery Charged

Hopefully by now you know if your battery is charged and you've charged it up if necessary. But how do you stop it going dead again?

Battery Tender

The answer is what's called a battery tender. It's similar to a battery charger in that it will charge your battery, but it's typically very low power. Rather than trying to charge your battery, it just tries to stop your battery discharging. If you leave it connected long enough, they can typically charge a battery....eventually! But that's not what they're usually designed for.

I used to use a battery tender on my ATV. At certain times of year it would be sitting there for months, and I would leave the battery tender connected 24/7 - that's what it's designed for!

If your vehicle is parked outside your house or in an RV park with electrical hookups, a Battery Tender Junior is a great option since it plugs into 110V. You can either connect it with battery clamps (like the jumper cables), or they often come with a wiring harness that you permanently attach to your vehicle's battery which exposes a quick-connecting plug you can use each time you want to plug it in.

You can also find higher power battery tenders that can charge a battery before automatically switching into maintenance mode to keep the battery topped off.

What about if, like us, you spend time boondocking where you don't have electrical hookups that you can leave a battery tender connected to 24/7?

Have a look at the solar battery tenders! These allow you to keep your battery topped off using a small solar panel - it doesn't take a big panel to keep a battery topped off! We have one of these sitting in our Amazon cart now, ready for when we're next in a spot where we can get an Amazon delivery. If you've used one of these, let us know in the comments below what you think of it!

Essential Off-Road Gear

Before you hit the trails for some off-road fun this summer, make sure you have the right gear.

Essential Off-Road Gear


It's a terrible feeling when you go to start your vehicle and the engine just won't start. But it's an even worse feeling if you don't have the tools you need to fix it.

A basic digital multimeter is a must-have tool for any RVer, but a plug-in 12V cigarette lighter volt meter will do much the same job and let you keep an eye on your battery. If your battery is low then run the engine to charge it up, but if it won't start then having a portable jump starter can really help!

Better yet, avoid the problem altogether and keep your battery in perfect condition using a battery tender - either a plug-in version or a solar battery tender for the times you're off-grid!

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