Upgrading The Lead Acid Battery To AGM Using This Stainless Box
Wet cell batteries are the oldest lead-acid technology, available in either serviceable or maintenance-free configurations. Sealed Lead Acid (SLA) or Valve Regulated Lead Acid (VRLA) variants offer a safer, more temperature-resilient alternative by sealing the unit to prevent electrolyte evaporation, prolonging lifespan, and reducing gassing. Absorbent Glass Mat (AGM) batteries improve on this by trapping the electrolyte in fiberglass mats rather than flooding the plates, making them entirely spill-proof and virtually immune to severe vibration.
If you are considering an AGM upgrade to increase Cold Cranking Amps (CCA), maximize engine bay space, and improve reliability, this guide covers why VRLA/AGM technology outperforms legacy wet cells. While a battery tray upgrade might not seem like the most exotic modification, the overbuilt design and engineering of the Rago Fabrication Battery Box deliver a significant leap in performance and flexibility over the flimsy OEM plastic tray. Though Rago explicitly designs these heavy-duty boxes for Group 31 and 34 sizes, this article will also show how a few minor adjustments let you easily run a Group 24 AGM battery.
Compatible with not only Toyota, but many other vehicles as well!
Find It Online
- Group 31 Battery Box
- Group 34 Battery Box (used in this post)
Use code – TRAILCO – to save 10%!
About Rago
Rago Fabrication has everything from roof racks, bumpers, MOLLE systems, and much more.
Rago was founded in April 2013 in a humble garage in Rancho Cucamonga, California, by Mario Rago after his service in the U.S. Navy as an Aviation Technician.
Before joining the military, Mario completed Toyota’s Technician Training & Education Network program and earned his ASE Certified Technician certification. He also gained hands-on training in metal fabrication and welding.
With his education, technical skill, and real-world experience, Mario began working as a full-time fabricator for a CORR race team. Later, a move to Texas led him to begin producing expertly crafted MOLLE panels, marking an important turning point for the business.
As demand grew, Rago Fabrication expanded from its beginnings inside the Rago home into a dedicated warehouse. There, the family purchased their first laser fabrication equipment and continued building the company with the same precision and dedication that started it all.
Today, Rago is under the Horsepower Automotive umbrella and offers a full range of products across multiple platforms, proudly carrying forward the same craftsmanship, effort, and attention to detail that began in that first humble garage.
AGM Battery Pros & Cons
Advantages
- Increased Safety & Flexible Installation: Completely spill-proof because the electrolyte is absorbed in fiberglass mats, allowing the battery to be mounted in almost any orientation.
- Faster Charging & High Power Output: Low internal resistance enables up to five times faster charging and delivers higher Cold Cranking Amps (CCA) for reliable engine starts under heavy accessory loads.
- Vibration & Shock Resistance: Built to withstand severe vibration, making them ideal for demanding applications like rock crawling, overlanding, and racing.
- Reduced Corrosion & Minimal Gassing: Eliminates the venting of acidic steam to prevent terminal corrosion, while producing minimal gas for safe use in enclosed compartments.
- Superior Temperature Tolerance: Performs better in extreme temperatures; the absorbed electrolyte won’t expand like a liquid if frozen, protecting the outer case from cracking.
- Low Self-Discharge & Stable Power: Retains charge significantly longer during periods of inactivity and maintains stable voltage under heavy loads.
- Extended Lifespan & Deep Discharge: Offers up to a seven-year lifespan (around 1,200 cycles) and allows up to an 80% Depth of Discharge (DoD), though keeping it above 50% is recommended for maximum longevity.
- Reduced Acid Stratification: Prevents internal acid stratification, eliminating premature degradation common in SLA batteries during partial charging or prolonged storage.
Disadvantages
- High Initial Cost: Advanced materials and production raise upfront prices, though this is mitigated by a significantly longer overall lifespan.
- Voltage Sensitivity: Highly sensitive to overcharging and excessive voltage, which increases the risk of thermal runaway (where trapped heat causes drying, melting, toxic chemical release, or explosion).
- Specialized Charging: Requires dedicated AGM-profile chargers that monitor voltage, current, and temperature; standard SLA chargers will under or overcharge the battery.
- Specialized Testing: Traditional or older diagnostic equipment relying on specific gravity measurements cannot be used to test AGM batteries.
- Greater Weight: Typically heavier than standard Sealed Lead Acid (SLA) equivalents.
- Limited Deep Cycle: Optimized for short bursts of high current rather than sustained deep-cycle applications, which can shorten their lifespan.
Features & Specs
Features
- Aircraft-grade 304 stainless steel.
- Stainless steel hardware for corrosion resistance.
- Compatible with a range of vehicles (4Runner, Tundra, Tacoma, and other trucks and SUVs, etc.)
- Rago rust-free guarantee.
- Protection on all sides of your battery.
- TIG-welded for a precise, snug fit.
- Group 34 AGM and SLA battery compatible, as well as Group 24, with additional spacers available at most hardware stores.
Specifications
- 304 stainless steel provides higher tensile strength (72,500 psi) than aluminum (45,000 psi), with superior shear moduli of 3770 ksi and 12,500 ksi, respectively, making it ideal for withstanding repeated impact stresses.
- 304 stainless steel is highly resistant to corrosion due to a protective oxide layer.
- Internal dimensions: 10.51″ (l) x 7.10″ (w) x 7.16″ (h)
- External dimensions: 10.67″ (l) x 7.26″ (w) x 7.16″ (h)
Adjusting Alternator Output Voltage (V)
As noted in the AGM pros and cons section, ensuring your alternator provides the correct voltage is critical. Standard Sealed Lead Acid (SLA) batteries optimize at approximately 14.2V to 14.4V, whereas AGM batteries require a higher charge profile, typically between 14.4V and 14.8V, meaning factory alternators leave them chronically undercharged.
The VoltageBoosterPRO Spark Edition for the Toyota Tundra addresses this via an adjustable, inline-fused diode modification that safely raises output. In testing on a 2017 Tundra SR5 TRD, “Low” mode delivered a 0.5V increase (averaging 14.4V), while “High” mode delivered a 0.7V to 0.8V increase (peaking at 14.9V). Matching your vehicle’s output to these specific charging requirements is essential for maximizing AGM performance, reliability, and lifespan.
Selecting Your AGM Battery
The table above was generated based on available 24F and 34R AGM batteries for the Tundra at the time of the article. Unfortunately, because the Tundra poles are reversed, the number of compatible batteries is reduced. I almost lengthened the battery cable just to expand my options, and may in the future. That said, there are still quite a few great options.
Color codes were assigned as green or red based on whether values were above or below the column average, with the exception of the final column on the right, which is a simple aggregate of the number of green boxes. Hopefully, this provides a convenient resource on your battery selection for your adventures. Don’t worry about the color codes and oversimplified ranking; this is just a quick and easy reference.
Performance Top 3
- XS Power Batteries D3400R
- Odyssey Extreme
- Fullriver Battery Full Throttle
Value Top 3
- Bosch S6 High Performance AGM
- Duracell Platinum
- Everstart Platinum
Benefits Of A Battery Box
Pictured above is an image from a Total Chaos Upper Control Arm (UCA) article highlighting issues with the OEM battery tray that Rago Fabrication has addressed.
Specifically, the Heavy Duty Battery Box is for you if you’re trying to…
- Use Group 31, 34 and 24 batteries.
- Reduce intrusion into the engine compartment to simplify maintenance and installation of aftermarket components, i.e., UCAs, as shown in the photo above.
- Provide additional containment capacity for leaks to increase protection to surrounding engine components.
- Increase safety by creating additional material around the battery to reduce the risk of damage to engine components in the event of a battery explosion.
- Increase rigidity and strength to reduce battery movement under off-road conditions.
- Increase drainage and reduce corrosion under the battery tray.
- Customize your engine bay with raw stainless or powder-coated in a customized color.
Unboxing & First Impressions
Rago nailed the packaging, and the box arrived in perfect condition. The thick stainless steel construction is incredibly rigid, featuring impeccable TIG welds, flawless machine work, and a perfect fit. Small details, like the signature Rago “R,” showcase the manufacturing pride and confidence behind the brand.
Compared to the OEM setup, this overbuilt design offers superior support. A true game-changer is the battery hold-down bracket, which applies evenly distributed pressure across the entire top of the battery rather than just contacting the edges. With its superior durability, craftsmanship, and clean look, this is an excellent, simple modification.
Installation
Tools Required
- 1/4 or 3/8 Ratchet
- 10mm Deep Socket
- 10mm Standard or Shallow Socket
- 4mm Hex Socket
- Metric 11mm or SAE 7/16 socket
Materials Required
- J-Hooks (If Required)
- 1/4 x 1/2 x 5/8 Stainless Steel Spacer (Group 31)
- 1/4 x 3/4 x 5/8 Stainless Steel Spacer (Group 24)
- 1/4-20 x 1 1/2 Hex Stainless Steel Bolt (Group 24)
- Blue Thread-Lock (Optional)
- Safety Glasses / Goggles
- Adhesive Rubber Strips (Optional)
Step 1. Lay All Items Out
It is always good to lay everything out before starting to ensure you have all the items shown above for a Group 34R installation. You do not want to remove your current battery for a core turn-in to find out that you don’t have the required hardware. I installed Group 24F and 34R batteries and listed specific items for each battery size in the parts section above that must be purchased separately.
Step 2. Disconnect Negative & Positive Battery Terminal
Wear safety glasses/goggles throughout this procedure. Never allow metallic tools to touch a terminal and any other metal surface simultaneously, as this can cause severe vehicle damage or a battery explosion.
- Disconnect Negative Terminal: Loosen the negative terminal clamp bolt using a 1/4″ ratchet and a 10mm socket, then remove the clamp. Position the negative cable safely away from both battery posts to prevent accidental contact.
- Disconnect Positive Terminal: Loosen the positive terminal clamp bolt using the same 1/4″ ratchet and 10mm socket, then remove the clamp. Position the positive cable safely away from the post to prevent accidental contact.
Step 3. Remove Battery Hold Down Bracket
Remove the battery hold-down bracket with a 1/4-inch ratchet and a 10mm deep 6-point socket. Retain the OEM front battery hold-down J-bolts (2) and nuts (2) for re-use and reinstallation in a later step. Be careful not to contact the battery posts when removing fasteners with the ratchet or socket.
Step 4. Remove Battery Tray
Remove the OEM white plastic battery tray. As you can see, it traps moisture and debris, which has damaged the paint and caused oxidation.
Step 5. Clean & Preserve Tray Area
You will probably want to clean the area under the tray, and potentially corrosion control (if required). The plastic OEM tray will not be reused. This is a good thing in my view, as it tends to trap moisture, which Rago Fabrication can help avoid with minimal effort.
Step 6. Apply Rubber Adhesive Strips (Optional)
To ensure adequate airflow and prevent water from trapping during off-road adventures, replacing the OEM plastic tray is essential. Even in dry climates like Southern California, a surprising amount of moisture collects beneath the factory setup, leading to hidden debris buildup. Adding rubber strips under the new tray addresses this perfectly by allowing drainage while providing critical impact dampening and extra grip to prevent shifting during high-speed runs.
Furthermore, this protective layer prevents the metal tray from chafing and damaging the engine bay paint—something the flimsy OEM tray had already begun to do.
Step 7. Install Rago Box & OEM J-Hooks
Install both OEM J-hooks removed in Step 4 above and the Rago Heavy Duty Battery Box.
Step 8. Group 34 & 34R Only, Install Fasteners & Spacers
For those prioritizing maximum CCAs and weight reduction over reserve capacity, the Group 34 size is ideal. Ensure you select a 34R rather than a standard 34 to match the Tundra’s reversed terminal locations, avoiding an incorrect fit and an extra trip to the store.
Because the Rago box is designed for a Group 34, the only required modification is using shorter J-hooks or a 1/4″ bore x 3/4″ OD x 1/2″ long stainless spacer to ensure proper thread engagement. Once the spacers or new J-hooks are in place, optionally apply blue thread locker, secure the bracket with the four provided Rago bolts and washers, and tighten.
Step 9. Group 24F Only, Install Fasteners & Spacers
If you prefer greater reserve capacity over slightly higher Cold Cranking Amps (CCA)—and don’t mind a few extra pounds—the Group 24 AGM battery is an excellent choice.
Because the Group 24 battery is taller than a standard Group 34, installing it in a Group 34 box requires a few extra components and steps:
- Six 1/4″ (bore) x 3/4″ (Outer Diameter) x 3/4 (Length) stainless spacers are required
Once the spacers or new J-hooks are in place, apply blue thread locker (optional), and install the longer 1/4-20 x 1 1/2 bolts (4), washers (4), and battery hold-down bracket, then tighten. Your battery may require shims to be adjusted; they’re easily obtained at most hardware stores or on Amazon.
Step 10. Group 34 & 34R Only, Install Hold-Down Bracket
Apply blue thread locker (optional) and use a 1/4-inch ratchet and an 11mm or 7/16-inch socket to install the extended-length bolt to secure the Rago Fabrication battery hold-down bracket.
Step 11. Connect Positive & Negative Battery Terminal
Safety First: Wear safety glasses/goggles throughout this procedure. Never allow metallic tools to touch a terminal and any other metal surface simultaneously, as this can cause severe vehicle damage or a battery explosion.
- Install Positive Terminal: Connect the positive terminal clamp. Tighten the bolt using a 1/4″ ratchet and a 10mm socket.
- Install Negative Terminal: Connect the negative terminal clamp to the battery post. Tighten the bolt using the same 1/4″ ratchet and 10mm socket.
Final Thoughts
The Rago Fabrication Group 34 Battery Box was the motivation I needed to do the AGM conversion I’ve been considering, and I can’t believe I waited this long. While marketed as a universal box that inherently requires some creativity, it easily accommodates both 24F and 34R sizes with minimal effort and inexpensive hardware/spacers. The quality completely outclasses the OEM tray.
Suggestions For Improvement
- Hardware: Include spacers for Tundra J-hooks and extended metric hex-head hardware.
- Shims: Provide HDPE or UHMWPE side shims to eliminate tedious spacer alignment and instantly officially support more battery sizes.
- Padding: Add rubber strips for extra protection.
However, these are minor tweaks for an otherwise killer product. I will absolutely be installing this in future vehicles. Highest recommendation!
