Lithium vs AGM Weight Comparison Calculator

Weight matter. How many times do you load a fully-packed van, only to realize that there’s no room for batteries? There they are in front of you, your brand-new Group 31 AGM battery, but it weighs a ton. Why isn’t my payload as high as it says in the brochure? It’s easy to fall into this newbie converter’s pitfall.

The mistake is buying batteries according to there amp-hour rating; the number printed on the battery itself. That’s a measure of capacity, not utility. Capacity has two parts: weight and usable capacity. A bank can be heavy but useless; it can run down before lunchtime. Alternatively, a bank can be light yet useful and keep the lights on all night long.

Why Weight Matters for Your Van

The point is that payload are limited. And recovering payload costs money. With that, you simply plug in your system voltage and your target energy and calculator (above) does the math for you. You no longer have to guess about conversions or coefficients. It makes sense if you change your perspective.

Stop thinking in terms of nameplate ratings. Start thinking in terms of usable energy. Say you have an AGM battery rated for one hundred amp-hours. You should of only plan to use half of that amount. Go over that and you run the very real risk of damaging the plates. With a lithium iron phosphate battery of equal nominal size, you can uses ninety percent of its capacity without shortening its life. That makes all the difference when trying to fit power into a tight space. It keeps you from breaking your axle.

The reserve margin input is that safety net for cloudy days or heavy loads. Sizing a bank to what you use in a day give you zero wiggle room. If it gets a few degrees colder or you have an extra long night at the campsite, you’re out of juice and flat on your ass. When you put 15-20% reserve into the mix, you’re carrying a bit more weight from the start. But you have some breathing room down the road. Not a bad trade off so you don’t wake up with a dead fridge.

The battery calculator throws that cushion onto your target and doesn’t begin calculating batteries until then. So resulting number isn’t a hypothetical best case scenario, but something closer to reality.

The other thing people forget about is there is some unseen weight in the installation hardware. Thick interconnect cables, a battery tray, shunt, bus bars, and proper hold-downs can all add up. These are the allowances included in the fields on the tool so you aren’t getting blindsided with fifty pounds of steel and copper. You may be changing out the chemistry so you save eighty pounds. But if you don’t account for the installation hardware, you realy only saved maybe fifty. Still good, but accurate.

You’re right at or over your gross vehicle weight rating for your vehicle. You’d like to know exactly what’s in it, how much weight it has, and where it sits in relationship to your axles. Where you put the weight matters as much as the overall amount. If you have a large battery bank, putting it near the rear of your trailer adds tongue weight which impacts towing dynamics. Bring the same weight forward into a van and it may impact handling through corners.

The good news about lithium banks is they’re lighter. So you can put them wherever works best for accessibility. Also, it lets you balance out vehicle to best effect. You don’t need to hang a dead weight anchor wherever it’s easiest. Instead, you can pick a location that makes sense for safety and for air flow. It also make it easier to service.

Now consider how this plays out in various voltage systems as shown by the reference table located on the page. For example, if you have a forty-eight volt system then you use fewer amps for the same amount of power. That equals thinner cables with less voltage drop over distance. To reach your desired capacity, you need fewer parallel strings, which means huge weight savings. Fewer batteries equal less complexity and fewer connection. This, in turn, gives less opportunity for a bad connection to become a fire hazard or a hot spot. As the available power goes up so does simplicity of the wiring.

The point really isn’t just having a battery bank. It’s having a power system you can rely upon without sacrificing carrying any other gear: food, water, etc. One pound less battery means one pound more whatever else. Perhaps it’s another 10 gallons of fresh water. Maybe it’s a beefier roof rack for bikes. There’s a tradeoff. And it’s always about what matters most to you.

Once you grasp that usable energy informs how you size things, you begin making better choices. You realize that weight only comes as a result of size. You quit getting hung up on amp-hour numbers and you manage energy. The battery is no longer an afterthought. Instead, it’s a planned part of your loadout. You go home with a working power system that fits your real life, instead of just your math.