When you’re comparing electric lawn mowers, you may find two comparable mowers at widely different price points. The reason for that, if you read the fine print, is frequently the battery type. The cheaper ones use lead acid batteries and the more expensive ones use lithium. So what’s the difference? Let’s compare lead acid vs lithium batteries.

Where the names lead acid and lithium come from

lead acid vs lithium batteries

You may be familiar with lead acid batteries from the traditional car battery. The technology has been around more than 150 years. Lithium batteries are a much newer technology.

Lead acid is the older technology, invented way back in 1860. Yes, eighteen. It’s the technology in a traditional car battery, and probably also in your computer’s UPS if you have one. It’s lead plates suspended in sulfuric acid acting as the electrolyte, hence the name lead acid. The reaction between the two chemicals can store and release electricity.

If you don’t like things invented after 1900, lead acid is the battery technology for you. You can use this loophole to operate a battery powered riding lawn mower. Be sure to tell your friends.

Lithium batteries are a category of technologies, rather than a single combination, but all of them involve a combination of lithium and other elements. They typically use an organic compound as an electrolyte instead of acid. Lithium batteries have circuitry that protect them from undercharge and overcharge, which increases their efficiency and life expectancy.

I’m a big fan of battery powered lawn mowers, especially when it comes to batteries vs gas. But part of the reason is because the push mower I bought uses lithium batteries. The people who bought riding lawn mowers with lead acid batteries a couple of years ago soured on them in year 2, when it was year 2 that really sold me on the idea of lithium powered lawn mowers.

Cost

Lead acid vs lithium batteries

Lithium batteries cost more up front than lead acid, which is why the tiny battery for my drill costs as much as the battery for my 2011 Toyota RAV4.

Cost is the most noticeable difference. Lithium batteries cost more than lead acid at least up front. If you see two riding lawn mowers that both claim to cut the same acreage on a single charge but one of them costs hundreds less than the other, chances are the cheaper one has a lead acid battery. You’ll pay less up front, but the lithium battery will need replacement less frequently and can run longer on a single charge, so in the long run the lead acid battery will probably cost more and will be less convenient, both in terms of runtime and ongoing maintenance.

In applications where you will charge and discharge the battery frequently, like solar power and lawn equipment, lithium ends up being cheaper in the long run because it doesn’t wear out as quickly.

Charging cycles in lead acid vs lithium batteries

You can run a lithium battery to 20 percent safely. You can only run a lead acid battery to 30 to 50 percent, and if you regularly exceed this, you shorten the useful lifespan of the battery. If you bought a riding lawn mower and it could cut your lawn on a single charge the first year but couldn’t do it anymore after the second, it’s because the lead acid battery in it is wearing out.

Lead acid is fine in a UPS, where you typically use it for short power interruptions, and probably only experience a long power interruption every few months. It’s a bigger problem in your lawn mower since you’ll be using it every weekend.

Weight

Lithium batteries weigh about 1/3 as much as lead acid. This is why your grandfather’s pea green Black and Decker drill had a cord. It wasn’t practical to put a lead acid battery in it. 90% of a lead acid battery is lead, but only 3% of a lithium battery is lithium. Lithium weighs less than lead, but there’s less metal in a lithium battery. The quantity makes a bigger difference than the weight of the metal.

Temperatures

Lithium batteries don’t like cold temperatures. That’s not a problem in a lawnmower, but it could be a problem in a snowblower. But it’s a tradeoff. You probably don’t want to keep your snowblower plugged in all year. So when you buy an electric snowblower at the big box store, that’s why it uses the same lithium ion battery system as a push mower.

Charge cycles in lead acid vs lithium

Lithium batteries charge faster.

You need to keep the lead acid battery charged at 95 to 100 percent when not in use. Lithium batteries prefer to sit at 70 to 80 percent.

It’s possible to retrofit lithium batteries in place of lead acid, but they charge at different rates, so you will also need to replace the charger. It’s typically more involved than just buying a new battery and dropping it in. It might be tempting to buy a cheap model and upgrade the battery later. But if you can afford the higher upfront cost, it’s cheaper to buy equipment with lithium batteries up front than it is to buy lead acid and upgrade later.