Replacing 100Ah Dragonfly Lithium Batteries with WattCycle 314Ah (628Ah total)

We are pleased to share this hands-on review written by Mr. Tom Westhoff, who tested WattCycle products in a real-world setup and documented his experience in detail. This article is published with his permission and appears here in his original first-person perspective. All views, observations, and conclusions expressed below are those of Mr. Tom Westhoff based on his own experience.

Here is the original article from Mr. Tom Westhoff:

Note: Since writing this document, WattCycle has released a heated version of this battery. If I were to do it today (March 2026) I would use the heated version. They also released a slightly larger physical size 314Ah

battery that may also fit which has a better BMS and the cover can be removed for servicing, not heated, but may be worth considering.

I’m sharing my experience replacing my two factory installed 100Ah Dragonfly (Battle Born) Lithium batteries with two WattCycle 314Ah Lithium batteries. If you follow this guide, you may find the job is easier than you probably thought it was.

This guide will also apply to other brands of batteries in the same physical form factor such as Kepworth, Sun Fun Kits, Epoch, and possibly others. Some of this will also help if you want to upgrade from lead acid or AGM batteries to Lithium batteries as well.

GOALS:

1) a minimum of 600Ah so I could run my Atmos 4.4 (TOSOT) A/C with my 2000W Xantrex inverter overnight if possible while boondocking, and most importantly so our dog Ella could stay in the RV safe and cool while we went shopping, visiting attractions, or eating in restaurants in the summer heat.

2) Blue Tooth App to monitor internal cells and BMS functions.

3) Batteries must fit into the same battery bay as the original Dragonfly batteries.

INTRODUCTION: Lithium batteries have been getting better in quality as well as coming down in price over the last several years. WattCycle recently introduced a new 314Ah Mini Lithium battery with 200A Battery

Management System (BMS) and Bluetooth phone app capability at a very reasonable price. About $549 each at the time of this writing. I bought a two-pack when on sale and paid about $1045 shipped to my door. I watched a video teardown for this battery and saw that it was built well and high quality which is not common with many of the lower priced brands. I decided to try these and see how they performed and save several thousand dollars in the process.

PreparaĦon:

1. The batteries arrived shipped to my house. The box was beat up a little, but no damage was seen and the batteries were packed well. I unboxed them and carried them to where I would be working.

Download the WattCycle phone app and install. Find both batteries on the app and re-name them so you know which one each is. I named mine by adding ‘One’ and ‘Two’ to the default number/name that was already given to the battery. You might use ‘Left’ and ‘Right’, or ‘Burt’ and ‘Ernie’ as well. The batteries do not come fully charged. Mine were 37% and 38% respectively.

Charge both batteries to 100% so they have the exact same voltage on the terminals. You can use a power supply or a lithium battery charger for this. If you don’t have a charger they are sold cheap on Amazon, and WattCycle sells one too that can be ordered with the batteries. Charging could take a long time as the batteries have a lot of capacity. Example: a 10A charger will take a 31.4 hours to charge one of these batteries from 0% to 100%.

2. Important >>> Next disable charging and discharging for both batteries using the app by tapping on the blue squares labeled ‘Charging’ and ‘Discharging’. In theory, when you do this, the batteries will not have any voltage on their terminals, although mine measured a few volts anyway. This will make reconnecting the cables safer and keep sparks from occurring if you accidentally short the terminals out. Nice to have an app to shut the battery off!

3. Shut off the RV power switch by the door. Shut off the inverter. If you have the factory solar panels cover them with something opaque because the factory installed solar panels do not have a disconnect switch. Use a black plastic garbage bag or a rug, for example. If you have a solar power switch shut it off.

This photo is what it looks like before beginning work. I had previously installed a Victron shunt, the blue shunt is mounted to the side of the bay separator. The thin red wire seen is the power wire for the shunt. If you don’t have the shunt ignore this.

4. The Dragonfly (Battle Born) batteries don’t have an ‘Off switch’ or any method to shut them off. Be very careful to not short out the positive terminal to the chassis or to the negative terminal of either battery. You may want to wrap metal wrenches in electrical tape if you are unsure of yourself.

Disconnect the long negative battery cable first. This is the safest way and reduces the possibility of sparks and damage. My battery bolts were ½” (13mm will work too). Then remove the cable connecting the two battery negative terminals. There will likely be a wire connected to a yellow plastic thing on one of the battery terminals. Pay attention to which terminal (+ or -) it is connected to. This will need to be reconnected on the new batteries if you are still using the factory DC-DC converter for charging the batteries. Mine was a 30A Sterling DC-DC charger. More about this later.

I temporarily covered the positive terminals with tape to guard against shorting the wrench to them while removing the negative terminal. After removing the negative cables, I used tape to cover the exposed battery terminals for safety.

5. Remove the long positive battery cable, and again cover the exposed lug with some tape to keep it from touching anything metallic. Move or tape the long cable out of the way temporarily so it doesn’t get in the way while working. My positive cable had some voltage on it, probably from the solar panels, so be mindful. Then remove the short cable connecting the two battery positive terminals.

Remove the small screws and the heater control wires from each battery. Tape the bare heater wire terminals and move them out of the way. Now both batteries should have nothing connected to them.

6. Disconnect the straps that are holding the batteries down, and remove the Dragonfly batteries and set them aside. Be careful not to short the battery terminals against the metal bay while removing them. I covered my battery terminals with tape before removing the batteries.

7. Remove both plastic battery hold down mounts and straps. There are six small sheet metal screws around the perimeter of each. Now the battery bay should be empty except for the red covered bus bar on the back wall, and the long positive and negative battery cables. Clean out the battery bay before proceeding. Mine was full of dust and dirt.

8. Now you need to determine how you will hold down the new batteries. The WattCycle’s are larger than the old Dragonfly’s. You could cut the old plastic hold down mounts into four pieces to fit the new batteries and remount them, as some others have done. I decided to make a new battery hold down using an aluminum bar and stainless steel ¼” threaded rod which I purchased at the local hardware store. At the end I will explain more details of how I made the new battery hold down.

Measure and check battery placement whatever mounting method you use. Leave some space between the batteries for air flow. I mounted the left battery as close to the left wall as I could. Spaced the second battery with about 1” space between the two batteries. That gave me some extra room on the right side for wires.

Important >>> be especially careful to make sure the battery on the right side sits far enough back so the compartment cover latch doesn’t hit the battery or the compartment won’t close. I test fit the batteries and moved them around until there was enough clearance to close and latch the compartment before installing my battery hold down. There is not much room front-to-back with the new bigger batteries because of the red bus bar assembly on the back wall. The batteries do fit though!

I cut some strips of ½” vinyl molding scraps I had, and put one horizontally across the back of the compartment to keep the batteries from moving too far back and hitting the red bus bar assembly. I cut out a small section on the rear piece, as you can see in the photo, so the ventilation slots in the rear would not be blocked. Another 5/8” wide strip was put along the front edge to keep the batteries from moving too close to the front to ensure the compartment latch would close properly (strip not seen in the photo). I bolted the strips through the bottom compartment metal using castle nuts to not have sharp edges on the bottom. I also added two strips of adhesive backed rubber stair tread to the bottom of the compartment to cushion the batteries and make them less likely to slip once snugged down.

At this point it would be a ‘good’ idea to check all of the connections on the bus bar assembly to make sure they are positioned straight, and torqued to 14Nm (10 ft lbs). They may possibly have become loose over time. Much easier to do it now, than later after the batteries are installed. When finished, flip the flexible red cover up and secure it so it covers the fuses and connection bolts. The thin red wire connected to the far-right lug is from the solar controller it has an inline fuse holder that is tucked in there you may want to untangle. Not the best way to do it, in my opinion.

9. Install the new batteries and check to make sure the compartment door closes and latches OK. Then install the aluminum bar and tighten the three battery hold down nuts (or straps), firm but not over tight.

10. Connect the MRBF fuse holder to the battery positive terminals and torque to 14Nm (10 ft lbs). Don’t forget the yellow terminal thing if there was one (not needed with Victron Orion XS DC-DC charger) and the positive little red wire for the Victron shunt if you have one. These terminals must be placed on top of the battery cable lug, not on the bottom.

Install the MRBF 300A fuses and Re-connect all of the positive battery cables finger tight. Then re- connect all of the negative battery cables finger tight.

Important >>> Connect the long positive and negative cables on opposite batteries. Positive cable on one battery and the negative cable on the other battery.

Do NOT connect both long cables to the same battery for best current sharing.

• Torque the MRBF fuse connections to 8.5Nm (6.3 ft lbs).
• Torque the other connections to 14Nm (10 ft lbs).

11. Check everything over to make sure it is correct. You are now done with the physical portion of the job!

12. When you are certain everything is connected correctly, go into the WattCycle app for the first battery and enable both charging and discharging.  Then use the app and do the same for the second battery. Wait a few seconds and verify that the app shows very little current flowing. If current is flowing wait for it to go close to zero as the batteries balance.

You are done. You now have 628Ah capacity. Everything should work as before. Try the following to help get used to the batteries and their phone app.

• Turn on a load in the coach, light all of the lights. After a minute you should see in the phone app that the batteries are discharging. Wait until the batteries get down to at least 95%. Plug into shore power or start the vehicle engine. The app should now show that the batteries are charging. When the batteries reach 100% you will see the app show that charging has been shut off on one or both of the batteries.
• Turn on your inverter. Run a small heater, toaster, or coffee pot. Look at the app and check that both batteries show they are discharging and supplying a good amount of current. If only one battery is discharging, go to the other battery and make sure the ‘Discharge’ button has been turned on. It will take several discharge and charge cycles before both batteries get completely in sync. It won’t hurt to  run a high power load until the batteries get below 50% and then let them charge back up a few times.

OBSERVATIONS:

After installing our WattCycle batteries we went on a 16 day camping trip to try them out. They worked very well! I am very pleased at the results. The Atmos A/C started and ran well on the inverter.

We ran our Atmos A/C many times in parking lots while shopping or eating in a restaurant, and the batteries/inverter worked great.

Note: We were the very first LTV to get the Atmos installed. Since it was the first one, a soft start was not installed as it was not supposed to be needed. However, we have had absolutely no problems running the Atmos on a 15A or 20A shore power, or with our 2000W Xantrex inverter. A soft start could of course be   installed at any time and may help.

At one campground, for a test of the new batteries, we didn’t connect to shore power at all, ran the A/C on the inverter all night from 6pm to 8am the next morning. The outside temperature was in the high 70’s (F). In the morning the batteries were at 63%. It did cool off during the night to around 70. When I got up in the morning, I went out and plugged into 30A shore power so I could charge the batteries free. The batteries were close to  90% when we left at 11am. After driving about an hour our 400W solar and DC-DC chargers had the batteries  at 100% again.

The WattCycle phone app allows you to see individual cell voltages of the battery if you press the voltage button. The app also shows the expected run time or charge time of the batteries for whatever the present load is. With fully charged batteries and the Atmos A/C running on high, with the compressor running, it showed 7.1 hours remaining. That would occur if the compressor stayed on constantly and didn’t cycle on/off which would be normal. Under normal conditions I expect to get 10+ hours of operation depending on outside temperature etc.

One thing to note is that having larger capacity batteries means they take longer to charge too.

I had previously swapped out my Sterling 30A DC-DC charger for an Orion XS 50A DC-DC charger which gives almost 50 amps charging when idling or driving. When installing these larger batteries, since I had everything torn apart anyway, I installed a second Orion XS 50A DC-DC charger. Now at idle (and driving) the batteries charge at around 97A. The Ford Transit alternator is rated at 250A so it can handle it easily.

Just as a test, when the batteries were low, I ran the generator while driving and the new batteries were charging at around 185A. Not too bad!

I had also previously installed a Victron shunt to monitor the Dragonfly batteries since they had no phone app or any way to judge the State of Charge (SOC). I am glad I kept the shunt. It shows the whole system as if there was one big battery and it complements the WattCycle phone app that monitors and controls each of the two batteries. The app also displays the voltages of the internal battery cells.

MAKING THE BATTERY HOLD DOWN:

I purchased a ¼” x 1 ¼” x 3’ aluminum bar at the local Ace Hardware store. I purchased a three foot, ¼” stainless steel (SS) threaded rod, and nine SS ¼” nylon insert lock nuts, and six SS ¼” washers at Home Depot.

The aluminum bar was cut to the width of both batteries as positioned in the compartment plus 1.5”. I drilled three ¼” holes in bar corresponding to the outside edge of the batteries (about ½” in from each end) and at  the center between the batteries.

The bar was laid flat on the bottom of the compartment midway between the front and the back, the holes in the bar was used as guides to drill ¼” holes through the bottom of the battery compartment.

The threaded rod was cut into three pieces, each with a length of the battery height plus 1.5”.

A nut was put on one end of each threaded rod, and the threads were superglued so the nut would not come off.

Each rod was inserted in a hole up from the outside of the bottom compartment. A washer and then a nut was threaded from the top of the rod all the way down to the bottom of the compartment and tightened to hold the rods securely in a vertical position. I used an electric drill with 7/16” socket on the bottom nut to turn the threaded rod which made getting the washer and nut to the bottom much easier.

The batteries were placed into final position between the threaded rods and checked to make sure the compartment latch closed correctly. The aluminum bar was then placed over the rods, and washers and nuts were threaded on each rod from the top, to snugly hold the bar against the batteries.