If you’re thinking about a prius second battery for your build, I’ll say this – you’re not the only one. I wanted bigger power for my Ultimate Overland Prius, and while a second battery sounds weird for a Prius, it opens up real options for off-grid and camping setups. More amps, more freedom. That said, finding the right battery and making it fit was a whole mission. :: sips tea ::
06/03/2021 UPDATE: 135A breakers have replaced the 120A Breakers. I finally found them!!
Seriously, tracking down a compact prius second battery with decent Ah (amp-hour) ratings is tougher than you’d think. Most batteries with real capacity are just too big for a Prius, so I spent weeks comparing options. What matters most is Ah, since it determines both runtime and how much power you can reliably pull before draining your battery down too low. Think about it: a battery marked 1Ah should deliver 1 amp steady for an hour, or 2 amps for half an hour, and so on, before it taps out.
My first step after all that research was test-fitting the spot I wanted. Why? Practically every “100Ah” AGM battery is just way too massive for my Prius. But then I found the right fit – a 12V 85Ah marine AGM SLA deep cycle battery that somehow squeezed in perfectly. Did it take some careful measuring? Absolutely. But having that real-world capacity means I can run everything longer, confidently, without risking damage or voltage drops that would make the system unreliable.
Since the install meant pulling out most of the trunk plastics, I decided to go further and dropped in a layer of Kilmat and then Noico car sound insulation. Community tip: If you’re doing a prius second battery upgrade, this is your chance to soundproof the area and keep those road vibes down. Trust me, once everything is bolted in, it’s a headache to pull it all apart again. My tie-down bracket made sure the battery wasn’t going anywhere.
I’m not done! The wiring and layout are still in progress with new 135A breakers, a 12-circuit fuse box, true isolator, and all the little pieces. Picking components for a prius second battery system can get tricky. This is where I lean hard on the community – IG DMs, forum questions, you name it, and real-world tips win every time. If you want to see other approaches and how people like me are getting serious about dual battery builds, check out my breakdown over on why a battery combiner is the best choice for toyota prius dual battery systems or sodium-ion upgrade for your 2009 prius hybrid battery.
If you want to geek out more on 12V mods, methods, or just not wreck your MPG with heavy gear, catch my buddies sharing their dual-battery journeys at why I chose an 80ah second battery over a power station for my prius travels. Part 2 is coming. Stay tuned and definitely let me know if you’re running something like this or have questions about the install.
FAQ on prius second battery
Why install a prius second battery? For me, it’s all about independent power off-grid and while camping. I don’t want my 12V system limiting my options when I want to run a fridge, lights, or a fan overnight. An extra battery gives you confidence and time before you need to start the car.
Does adding a second battery hurt MPG? Technically, any extra weight can hurt MPG, but if you choose wisely and go AGM or lithium, it’s a pretty minor hit — far less than what a roof rack or big all-terrain tires do to your efficiency. Aerodynamics = king for max MPGs.
Best spot for a prius second battery? I ended up using the corner trunk area, but honestly, it comes down to your exact Prius generation and goals. Just be prepared to get creative — measuring twice, cutting once — and don’t be afraid to ask the community for what’s worked. Got more questions? Drop them below or DM me on IG.
Like what you see and want to dig deeper? Don’t forget to check the in-depth breakdowns on why swapping a JDM Corolla engine into a Prius isn’t plug and play. Community, keep the questions and support coming!
