If you own a Subaru with a start-stop system, you may be shocked when you replace the battery. Not because there’s any danger of electrocution, but because Subaru charges a shocking amount of money for their enhanced flooded battery. When people are hit with an unpleasant surprise, they generally have questions. In this article, we’re going to do our best to answer all of them.
- What’s so special about this battery?
- Can I just put a regular battery in instead?
- Why is Subaru telling me I have to buy a new battery tray and cover?
- Are there any cheaper options?
- Which is better, enhanced flooded or absorbed glass mat (AGM)?
What is an enhanced flooded battery?
If your Subaru has a stop-start system, it originally came with an enhanced flooded battery. Let’s start by defining a flooded battery. A flooded lead-acid battery consists of positive and negative lead-based plates submerged in a liquid electrolyte. The battery’s construction includes separators between the plates to prevent short circuits, while the electrolyte facilitates the chemical reactions needed to store and release electrical energy. This is the most common type of automotive battery.
So now we’ve covered “flooded,” but what’s “enhanced”? An enhanced flooded battery is more durable than a standard flooded battery—that’s pretty much it. The plates are thicker, there’s additional insulation, and they’re engineered to recharge faster. Another feature that’s important is a tip/tilt sealing mechanism in the lid to prevent acid from spilling out. This is very important for vehicles where the battery is mounted in the cab or trunk. They also typically have a higher CCA (cold cranking amps) rating per group size than a standard flooded battery.
Can I replace my Subaru’s battery with a standard group 35 battery?
Yes, you can replace your enhanced flooded battery with a standard flooded battery, but it won’t last long. Here’s why:
Your Subaru will stop and start many more times than a typical car per trip, so the battery will need to work much harder. In a typical car, you start the engine once and then drive for some time while the alternator gently recharges the battery—a relatively easy life for the battery. However, your Subaru may restart the engine 50, 100, or even 200 times in a single trip. That’s a lot of extra work.
An enhanced flooded battery is designed to handle nearly three times as many charge/discharge cycles as a standard battery. You might think that you’ll get one-third of the life if you buy a standard battery and that maybe it’s worth it for the cost savings. However, you may not even get that much life out of it. You’ll be asking the standard battery to perform beyond its capabilities, and it may not hold up.
Now, if you have the option to turn off stop/start, could you use a regular battery? Sure, why not. However, it’s hard to say whether the increase in fuel consumption would offset the price difference between batteries.
Why do I have to buy a new battery tray and cover?
On some Subaru models, Subaru decided that the original factory-installed battery was slightly underrated. As a result, they discontinued it and replaced it with a higher-rated battery that’s slightly larger. The new replacement battery does not fit in the original tray, and the original cover doesn’t fit over it either. So if you own one of these models and opt to buy the replacement from Subaru, you’ll also need to purchase the updated tray and cover.
Are there any other options for Subaru battery replacement?
Is it necessary to buy a replacement battery from the Subaru dealer if your vehicle is equipped with a stop/start system? Luckily, no—there is another option. AGM batteries are well-suited for vehicles with stop/start systems. Unfortunately, they are also expensive but still not quite as costly as buying an enhanced flooded battery from the dealer.
Which is better, enhanced flooded or AGM?
AGM batteries are actually superior to enhanced flooded batteries for vehicles with stop/start systems. Enhanced flooded batteries are considered a cost-effective option for these systems but don’t perform as well as AGM batteries overall. (1) Also, because enhanced flooded batteries are not very popular, they can be difficult to source on short notice. AGM batteries, on the other hand, are widely available. Here’s what makes AGM better:
- They allow for faster charging
- Sealed and pressurized. No liquid acid means no acid leaks
- Longer life
- More powerful
- Truly maintenance free
- Better tolerance of deep-cycling
The only category that enhanced flooded wins is cost, but that doesn’t really translate for people looking for a replacement battery due to the low availability of EFBs and limited purchasing options.
More reading
I found this article from Yuasa battery that covers AGM, gel batteries, and enhanced flooded batteries. Yuasa is a major manufacturer of high-quality motorcycle (and other) batteries and an authoritative source of information. If you have any doubts as to the superiority of AGM over enhanced flooded, please check the article.
In this impressive Google doc, a guy named Martin on Reddit spent a lot of time researching an alternative replacement battery for his Camry Hybrid (2012-2017). While not a Subaru with stop/start, many Toyota hybrids require enhanced flooded or AGM batteries in sizes not available in the US, except from Toyota dealerships. Martin performed a great public service by making this information available to all in very through DIY format.