Welcome to another Two-Minute Tech Tip Tuesday, brought to you by the National RV Training Academy (NRVTA)—America’s largest hands-on RV training school. This week, Todd is on location answering a tricky but important question:
“How can I tell how much life is left in a lithium battery when buying a used RV?”
Whether you’re eyeing a used Winnebago or any RV outfitted with lithium batteries, knowing the battery’s condition can save you hundreds—or even thousands—of dollars. So let’s dive into how you can assess the health of RV lithium batteries.
First Things First: Know What a Battery Cycle Is
A battery cycle is simple: it’s one full discharge followed by a full recharge. Every lithium battery has a rated number of cycles it can handle—anywhere from 3,000 to 10,000+, depending on the brand and quality.
But how do you see how many cycles are already used?
1. Bluetooth Monitoring (If Available)
Some modern lithium batteries (like Big Beard Battery or Battle Born) come with built-in Bluetooth connectivity. This is the easiest method. Just connect via their app and check:
- Total cycle count
- Current voltage
- Battery temperature
- Amp draw and other stats
If the battery supports this, it’s your best first step.
2. Internal Resistance Testing (Advanced & Expensive)
If you’re serious about testing batteries (like the pros), you can measure internal resistance. Higher resistance typically means an aging battery.
But here’s the catch:
You’ll need an internal resistance tester that costs $2,000–$3,000. Not ideal for the average RV buyer.
So let’s talk about what you can do…
3. Manual Capacity Test – Simple DIY Method
Here’s a straightforward way to estimate remaining capacity:
Step-by-step:
- Fully charge the battery.
-
Connect a known electrical load.
Example: Two fans pulling a total of 6 amps. - Use an amp clamp to measure the current draw.
- Run the fans and time how long they last.
Let’s say your battery is rated at 100 amp hours (Ah). You never want to drain lithium below 20%, so use 80% of capacity, or 80 Ah.
If you’re drawing 6 amps/hour:
80 Ah ÷ 6 amps = ~13.3 hours
If the battery powers your fans for about 13 hours, it’s performing well. If not, it might be time to replace—or supplement—it.
4. Check Resting Voltage
Another quick test:
Let the battery rest (unplugged and unused) and then measure the resting voltage with a multimeter.
Healthy lithium batteries typically rest around 13.2V–13.4V when fully charged. Lower than that might mean capacity loss—but it’s just one piece of the puzzle.
5. Ask the Owner
Sometimes the simplest answer is the best. Just ask:
- When were the batteries installed?
- What brand and model are they?
- Have they had any issues?
Then look up the manufacturer’s cycle rating—some go 4,000, 5,000, even up to 10,000 cycles.
6. Does It Meet Your Needs?
At the end of the day, the best test is: does the battery meet your power needs?
If it powers your appliances long enough for your lifestyle, it might not matter how old it is. And remember—with lithium, you can always add more batteries later. No need to replace everything at once.
Final Thoughts from Todd
Testing lithium battery life isn’t always easy. Some tools are expensive, and the information isn’t always visible. But with a little effort—like running a manual capacity test or checking resting voltage—you can get a solid idea of what you’re working with.
And remember: supply vs. demand is what matters most.
If your current system powers what you need, when you need it, you’re good to go. If not, consider adding another battery or upgrading when your budget allows.
That’s your Tech Tip Tuesday from the National RV Training Academy. Stay powered up, friends!
Want more RV tech tips?
Subscribe to our YouTube channel so you don’t miss the next hands-on lesson from Todd and the rest of the NRVTA team.